Organometallic solution based high resolution patterning compositions and corresponding methods

ABSTRACT

Organometallic radiation resist compositions are described based on tin ions with alkyl ligands. Some of the compositions have branched alkyl ligands to provide for improved patterning contrast while maintaining a high degree of solution stability. Blends of compounds with distinct alkyl ligands can provide further improvement in the patterning. High resolution patterning with a half-pitch of no more than 25 nm can be achieved with a line width roughness of no more than about 4.5 nm. Synthesis techniques have been developed that allow for the formation of alkyl tin oxide hydroxide compositions with very low metal contamination.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional patent application62/067,552 filed on Oct. 23, 2014 to Meyers et al., entitled “Organo-TinCompounds for Forming High Resolution Radiation Patternable Films,Precursor Compounds and Solutions, and Corresponding Methods,” and toU.S. provisional patent application 62/119,972 filed Feb. 24, 2015 toMeyers et al., entitled “Organo-Tin Compounds for Forming HighResolution Radiation Patternable Films, Precursor Compounds andSolutions, and Corresponding Methods,” both of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The invention relates to radiation-based methods for the performance ofpatterning materials using an organometallic coating composition. Theinvention further relates to precursor solutions that can be depositedto form organometallic coatings that can be patterned with very highresolution with radiation and to the coated substrates and coatingsformed with the precursor solutions before and after patterning.

BACKGROUND OF THE INVENTION

For the formation of semiconductor-based devices as well as otherelectronic devices or other complex fine structures, materials aregenerally patterned to integrate the structure. Thus, the structures aregenerally formed through an iterative process of sequential depositionand etching steps through which a pattern is formed of the variousmaterials. In this way, a large number of devices can be formed into asmall area. Some advances in the art can involve that reduction of thefootprint for devices, which can be desirable to enhance performance.

Organic compositions can be used as radiation patterned resists so thata radiation pattern is used to alter the chemical structure of theorganic compositions corresponding with the pattern. For example,processes for the patterning of semiconductor wafers can entaillithographic transfer of a desired image from a thin film of organicradiation-sensitive material. The patterning of the resist generallyinvolves several steps including exposing the resist to a selectedenergy source, such as through a mask, to record a latent image and thendeveloping and removing selected regions of the resist. For apositive-tone resist, the exposed regions are transformed to make suchregions selectively removable, while for a negative-tone resist, theunexposed regions are more readily removable.

Generally, the pattern can be developed with radiation, a reactive gas,or liquid solution to remove the selectively sensitive portion of theresist while the other portions of the resist act as a protectiveetch-resistant layer. Liquid developers can be particularly effectivefor developing the latent image. The substrate can be selectively etchedthrough the windows or gaps in the remaining areas of the protectiveresist layer. Alternatively, desired materials can be deposited into theexposed regions of the underlying substrate through the developedwindows or gaps in the remaining areas of the protective resist layer.Ultimately, the protective resist layer is removed. The process can berepeated to form additional layers of patterned material. The functionalinorganic materials can be deposited using chemical vapor deposition,physical vapor deposition or other desired approaches. Additionalprocessing steps can be used, such as the deposition of conductivematerials or implantation of dopants. In the fields of micro- andnanofabrication, feature sizes in integrated circuits have become verysmall to achieve high-integration densities and improve circuitfunction.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a coating solutioncomprising an organic solvent and a first organometallic compoundrepresented by the formula RSnO_((3/2−x/2))(OH)_(x) where (0<x<3) withfrom about 0.0025M to about 1.5M tin in the solution, where R is analkyl group or cycloalkyl group with 3-31 carbon atoms, where the alkylor cycloalkyl group is bonded to the tin at a secondary or tertiarycarbon atom.

In a further aspect, the invention pertains to a coating solutioncomprising an organic solvent, a first organometallic compoundrepresented by the formula RSnO_((3/2−x/2))(OH)_(x) where (0<x<3), whereR is an alkyl group or cycloalkyl group with 3-31 carbon atoms, wherethe alkyl or cycloalkyl group is bonded to the tin at a secondary ortertiary carbon atom, and a second organometallic compound distinct fromthe first organometallic compound and represented by the formulaR′SnO_((3/2−x/2))(OH)_(x) where (0<x<3), where R′ is a linear orbranched alkyl or cycloalkyl group and wherein R and R′ are not thesame.

In another aspect, the invention pertains to a method for patterning afilm on a substrate, the method comprising:

exposing the film with EUV doses of no more than about 80 mJ/cm²; and

developing the film to form features at half-pitch no more than about 25nm and linewidth roughness no more than about 5 nm.

In an additional aspect, the invention pertains to a method forpatterning an organometallic film on a substrate, the method comprising:

exposing the organometallic film to EUV radiation at a dose-to-gel valueof no more than about 15 mJ/cm² to obtain a contrast of at least about6.

Moreover, the invention pertains to a patterned structure comprising asubstrate having a surface and a coating associated with the surfacewherein at least portions of the coating are represented by theformulation (R)_(z)SnO_(2−z/2−x/2) (OH)_(x) (0<(x+z)<4), where R is analkyl group or cycloalkyl group with 3-31 carbon atoms, where the alkylor cycloalkyl group is bonded to the tin at a secondary or tertiarycarbon atom.

In a further aspect, the invention pertains to a solution comprising asolvent and a compound represented by the formulaRSnO_((3/2−x/2))(OH)_(x) where (0<x<3), where R is an alkyl, cycloalkylor substituted alkyl moiety having from 1 to 31 carbon atoms, thesolution having individual concentrations of contaminant metals of nomore than about 1 ppm by weight.

Additionally, the invention pertains to a method for synthesizing acompound represented by the formula RSnOOH or RSnO_((3/2−x/2))(OH)_(x)(0<x<3), where R is an alkyl or cycloalkyl moiety having from 1 to 31carbon atoms, the method comprising:

hydrolyzing a precursor composition having the formula RSnX₃, where Xrepresents a halide atom (F, Cl, Br or I), or amido group(s), orcombinations thereof wherein the hydrolysis is performed with sufficientwater to effectuate the hydrolysis, wherein the hydrolysis product hasindividual concentrations of metals other than tin of no more than about1 ppm by weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a radiation patternedstructure with a latent image.

FIG. 2 is a side plan view of the structure of FIG. 1.

FIG. 3 is a schematic perspective view of the structure of FIG. 1 afterdevelopment of the latent image to remove un-irradiated coating materialto form a patterned structure.

FIG. 4 is a side view of the patterned structure of FIG. 3.

FIG. 5 is a schematic perspective view of the structure of FIG. 1 afterdevelopment of the latent image to remove irradiated coating material toform a patterned structure.

FIG. 6 is a side view of the patterned structure of FIG. 5.

FIG. 7 is a side plan view of the patterned structure of FIGS. 3 and 4following etching of the underlayer.

FIG. 8 is a side plan view of the structure of FIG. 7 following etchingto remove the patterned, condensed coating material.

FIG. 9 is a side plan view of a “thermal freeze” double patterningprocess flow. The process shown in FIGS. 1-3 is repeated after a bakethat renders the first layer insoluble to the second layer.

FIG. 10 is a plot of weight loss as a function of temperature in athermogravimetric analysis.

FIG. 11 is a plot of mass spectral analysis as a function of sampletemperature performed in combination with the thermogravimetric analysisof FIG. 10.

FIG. 12 is histogram showing a particle size distribution obtained froma dynamic light scattering analysis.

FIG. 13 is a plot of a representative time correlation function from thedynamic light scattering measurement used to obtain particle sizedistributions such as that of FIG. 12.

FIG. 14 is a representative ¹¹⁹Sn NMR spectrum of a solution of compound1 as described in Example 3.

FIG. 15 is a representative ¹H NMR spectrum of a solution of compound 1as described in Example 3.

FIG. 16 is a plot of intensity as a function of mass-to-charge ratio ofa electrospray mass spectrometry experiment on compound 1 as describedin Example 3.

FIG. 17 is a plot of contrast as a function of dose-to-gel for threedifferent coating compositions having distinct alkyl ligands (n-butyl,iso-propyl and t-butyl).

FIG. 18 is a scanning electron micrograph of a silicon wafer patternedwith t-butyl tin oxide hydroxide following exposure using 13.5-nmwavelength EUV radiation pattern of 17-nm lines on a 34-nm pitch andfollowing development.

FIG. 19 is a scanning electron micrograph of a silicon wafer patternedwith iso-propyl tin oxide hydroxide following exposure using 13.5-nmwavelength EUV radiation in a bright-field pattern of 22-nm contactholes on a 44 nm pitch with a +20% bias and following development.

FIG. 20 is a series of SEM micrographs for 6 different formulation withvarious combinations of iso-propyl tin oxide hydroxide and/or t-butyltin oxide hydroxide patterned following exposure using 13.5-nmwavelength EUV radiation pattern of 17-nm lines on a 34-nm pitch andfollowing development.

FIG. 21 is a plot of dose-to-size plotted as a function of coatingcomposition for formulations A-F used to obtain the micrographs in FIG.20.

FIG. 22 is a ¹H NMR spectrum of i-PrSn(NMe₂)₃ prepared as described inExample 7.

FIG. 23 is a ¹¹⁹Sn NMR spectrum of i-PrSn(NMe₂)₃ prepared as describedin Example 7.

FIG. 24 is plot of weight as a function of temperature in athermogravimetric analysis of a sample of isopropyl tin oxide hydroxideprepared by Method 1 in Example 7.

FIG. 25 is a mass spectral analysis performed in conjunction with thethermogravimetric analysis of FIG. 24.

FIG. 26 is plot of weight as a function of temperature in athermogravimetric analysis of a sample of isopropyl tin oxide hydroxideprepared by Method 2 in Example 7.

FIG. 27 is an SEM micrograph of a silicon wafer patterned with isopropyltin oxide hydroxide synthesized using Method 1 of Example 7 followingexposure to EUV radiation at an imaging dose of 60 mJ cm⁻², withresulting 14.5 nm resist lines patterned on a 34 nm pitch with an LWR of2.9 nm.

FIG. 28 is a plot of weight as a function of temperature in athermogravimetric analysis of a sample of isopropyl tin oxide hydroxideformed using the process of Example 10.

FIG. 29 is a mass spectral analysis performed in conjunction with thethermogravimetric analysis of FIG. 28.

FIG. 30 is a ¹H NMR spectrum of t-AmylSn(C≡CPh)₃ synthesized by themethod of Example 11.

FIG. 31 is a ¹¹⁹Sn NMR spectrum of t-AmylSn(C≡CPh)₃ synthesized by themethod of Example 11.

FIG. 32 is a ¹¹⁹Sn NMR spectrum of t-amyl tin oxide hydroxidesynthesized as described in Example 11.

FIG. 33 is a ¹H NMR spectrum of t-amyl tin oxide hydroxide synthesizedas described in Example 11.

FIG. 34 is a set of SEM micrographs of silicon wafers with isopropyl tinoxide hydroxide (right images) or t-butyl tin oxide hydroxide (leftimages) exposed to 30-kEV electron beam and developed at a pitch of32-nm (top) and 28-nm (bottom).

FIG. 35 is a set of two SEM micrographs of a silicon wafer patternedwith isopropyl tin oxide hydroxide following exposure to EUV radiationand development for positive tone imaging with 100-nm (a) pitch and60-nm (b) pitch.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that organo-tin compounds with bonds to alkylgroups, especially branched alkyl groups (including cyclic ligands), canbe used as improved radiation patterned precursor film formingcompounds. Films formed with the compounds can be patterned withdesirable doses of radiation to achieve very high resolution patterns.The ligand structure for the organo-tin compounds provides for goodprecursor solution stability and good radiation sensitivity upon forminga coating. While alkyl-tin compounds with branched alkyl ligands havebeen found to provide for particularly improved patterning at lowerradiation doses, use of a mixture of alkyl ligands provides for furtherpotential improvement through the engineering of several features of theresulting coatings facilitating patterning. Desirable features ofcoatings formed with the organometallic precursor solutions provide forlarge radiation absorption and superior direct patterning for theformation of a patterned metal oxide coating. Precursor solutions withlow metal contamination, distinct from the metal, for example, tin, orcombination of metals comprising the organometallic coating composition,provide for coating formation useful for applications where metalcontamination can be unsuitable for the associated materials anddevices. Appropriate processing techniques for the formation of lowcontaminant precursor solutions are described. Precursor solutions canbe coated using appropriate techniques. Radiation patterning anddevelopment of the latent image can be performed to achieve images witha high degree of resolution and low line width roughness with very smallpattern features.

Exposure to radiation alters the composition of the irradiatedorganometallic coating material, disrupting the structure defined by thealkyl ligands and permitting further condensation and reaction withmoisture from any source, such as ambient moisture. On the basis ofthese chemical changes dissolution rates may vary substantially betweenirradiated and non-irradiated portions of the film with selection ofappropriate developer compositions, facilitating either negative tonepatterning or positive tone patterning with the same coating in someembodiments. In negative patterning, exposure to radiation and potentialsubsequent condensation converts the irradiated coating material into amaterial that is more resistant to removal with organic solvent-baseddeveloper compositions relative to the non-irradiated coating material.In positive patterning, exposure sufficiently changes the polarity ofthe exposed coating material, e.g., increasing the polarity, such thatthe exposed coating material can be selectively removed with an aqueoussolvent or other sufficiently polar solvent. Selective removal of atleast a portion of the coating material can leave a pattern whereregions of coating have been removed to expose the underlying substrate.After development of the coating following irradiation, the patternedoxide materials can be used for facilitating processing in deviceformation with excellent pattern resolution. The coating materials canbe designed to be sensitive to selected radiation, such as extremeultraviolet light, ultraviolet light and/or electron beams. Furthermore,the precursor solutions can be formulated to be stable with anappropriate shelf life for commercial distribution.

The metal ions generally also are further bound to one or moreoxo-ligands, i.e., M-O and/or hydroxo-ligands, i.e., M-O—H, in additionto the organic ligands. The alkyl ligands and the oxo/hydroxo ligandsprovide desirable features to precursor solution and correspondingcoating by providing significant control over the condensation processto a metal oxide with resulting significant processing, patterning, andcoating advantages. The use of organic solvents in the coating solutionssupports the stability of the solution, while the non-aqueous solutionbased processing maintains the ability to selectively develop theresulting coating following the formation of a latent image withexcellent development rate contrast, for both positive tone patterningand negative tone patterning due to the change in solubility of theexposed regions relative to the unexposed regions. Desirable precursorsolutions with dissolved alkyl-stabilized metal ions provide forconvenient solution based deposition to form a coating that can havehigh radiation sensitivity and excellent contrast with respect to etchresistance to allow for fine structure formation. The design of theprecursor composition can provide for the formation of a coatingcomposition with a high sensitivity to a particular radiation typeand/or energy/wavelength.

The ligand structure of the precursor organometallic compositions arebelieved to provide the observed desirable stability of the precursorsolutions as well as the radiation patterning function. In particular,it is believed that the absorption of radiation can provide for thedisruption of the bonds between the metal and the organic ligands tocreate a differentiation of the composition at the irradiated andnon-irradiated sections of the coated material. This differentiation canbe further amplified by suitable processing of the exposed film prior todevelopment, after development, or both. Thus, the compositional changesto form the improved precursor solutions also provide for improveddevelopment of the image. In particular, the irradiated coating materialmay result in a stable inorganic metal oxide material with a tunableresponse to the developer.

Through proper developer selection either positive or negative-toneimages can be developed. In some embodiments, suitable developersinclude, for example, 2.38% TMAH, i.e., the semiconductor industrystandard. The coating layers can be made thin without pattern lossduring development from removing the coating material from regions wherethe coating material is intended to remain following development.Compared to conventional organic resists, the materials described hereinhave extremely high resistance to many etch chemistries for commerciallyrelevant functional layers. This enables process simplification throughavoidance of intermediate sacrificial inorganic pattern transfer layersthat would otherwise be used to supplement the patterned organic resistswith respect to the mask function. Also, the coating material canprovide for convenient double patterning. Specifically, following athermal treatment, patterned portions of the coating material are stablewith respect to contact with many compositions including furtherprecursor solutions. Thus, multiple patterning can be performed withoutremoving previously deposited hard-mask or resist coating materials.

The precursor solution comprises polynuclear metal oxo/hydroxo cationsand alkyl ligands. The oxo/hydroxo ligands can be introduced through thehydrolysis of corresponding compounds with halide, amido, or alkynidoligands. Metal oxo/hydroxo cations, also described as metal suboxidecations, are polyatomic cations with one or more metal atoms andcovalently bonded oxygen atoms. Metal suboxide cations with peroxidebased ligands are described in U.S. Pat. No. 8,415,000 to Stowers et al.(the '000 patent), entitled “Patterned Inorganic Layers, Radiation BasedPatterning Compositions and Corresponding Methods,” incorporated hereinby reference. Aqueous solutions of metal suboxides or metal hydroxidescan tend to be unstable with respect to gelling and/or precipitation. Inparticular, the solutions are unstable upon solvent removal and can formoxo-hydroxide networks with the metal cations. Incorporation of aradiation-sensitive ligand such as peroxide into such a solution canimprove stability, but the background instability associated withnetwork formation may persist. Any uncontrolled network formationeffectively decreases the radiation sensitivity and/or development ratecontrast of the coated material by providing a development ratedetermining pathway independent of irradiation. The use of alkyl ligandsas a radiation sensitive ligand has been found to provide for improvedprecursor solution stability while providing for large radiationabsorption and excellent contrast for formation of very fine structures.

As described herein, the use of branched alkyl ligands, such astert-butyl or isopropyl, have been found to exhibit improved patterningperformance relative to unbranched alkyl ligands. While the use ofbranched alkyl groups have been found to provide desirable patterningperformance, in some embodiments, suitable mixtures of alkyl-tincompounds with Sn—C bonds to branched and/or unbranched alkyl groups, inparticular with at least one branched alkyl group, can be formulated tofurther improve nanolithographic patterning performance. It is believedthat the additional flexibility afforded by a mixture of alkyl ligandstructures allows the selection of multiple composition properties thatmay not be accessible within a single ligand structure: e.g. stability,solubility, radiation sensitivity, size, etc. Thus the formulation ofmixed metal ions with distinct alkyl ligands in the precursorcompositions may provide the basis for a range of improved performanceparameters, including the desirable patterning dose and line-widthroughness values demonstrated in a subsequent example.

The use of organo-metal compounds for radiation resist coatings isdescribed generally in published U.S. patent application 2015/0056542 toMeyers et al. (“the '542 application”), entitled “OrganometallicSolution Based High Resolution Patterning Compositions,” incorporatedherein by reference. The '542 application exemplifies n-butylSnOOH anddi-vinylSn(OH)₂ compositions for the formation of a radiation sensitivepatterning layer, and describes the desirability of alkyl ligandsinvolving compounds with tin, indium, antimony or a combination thereof.These general compositions are relevant for appropriate embodimentsdescribed herein. It has been discovered that branched alkyl ligands,such as tert-butyl, isopropyl, or tert-amyl (1,1-dimethylpropyl)attached to tin, and branched at the carbon of tin attachment (α-carbonbranched), can be effectively used as radiation patterning resists withlower radiation doses than those containing unbranched ligands.Similarly, other alkyl and cyclo-alkyl ligands branched at the α-carbon,including 2-butyl, cyclohexyl, cyclopentyl, cyclobutyl, cyclopropyl,1-adamantyl, and 2-adamantyl are contemplated, and within the scope ofthe present disclosure along with mixtures of compounds with alkylligands as describe herein. In other words, the resists with branchedorganic ligands contain alkyl or cycloalkyl ligands bonded to the Snatom via secondary or tertiary carbon atoms, RSnO_((3/2−x/2))(OH)_(x),(0<x<3), where R is a secondary or tertiary alkyl or cycloalkyl groupwith 3 to 31 carbon atoms. Alternatively, this composition may beexpressed as R₁R₂R₃CSnO_((3/2−x/2))(OH)_(x), (0<x<3), where R₁ and R₂are independently an alkyl group with 1-10 carbon atoms, R₃ is hydrogenor an alkyl group with 1-10 carbon atoms in which R₁, R₂ can form acyclic carbon chain as well as R₃ optionally also in a cyclic carbonstructure where the ranges of carbon atoms are additive if a cyclicstructure. A person or ordinary skill in the art will recognize that theorder of the R₁, R₂ and R₃ is essentially arbitrary, so that acomparison of groups in different compounds can take into account anarbitrary reordering and does not change the compound or associatedcomparison of the compound. In the same concept, a compound does notavoid the scope of this formula through the arbitrary assignment of an Hto R₁ or R₂ rather than R₃ since the formula instructs the associationof a single H with R₃. While not wanting to be limited by theory, it isbelieved that the structure of these branched alkyl ligands facilitatescleavage of the Sn—C bond during exposure, thereby increasing thesensitivity of the resist to radiation. This facilitation may beattributable to the increased stability of secondary and tertiary alkylradical or carbocation intermediates relative to related primary alkylmoieties. While not directly documented in Sn—C radiolysis studies,similar properties are evident in tabulated C—H bond-dissociationenergies. Thus, the improved compositions described herein provide forsignificant commercial advantages through lower radiation processing toachieve high resolution patterns with low line width roughness. Highresolution patterns with low line width roughness can thus be achievedwith lower radiation doses for processing improvements relative tosimilar superior resolution and low line with roughness achieved withmetal oxide based photoresists with peroxide based ligands, as describedin the '000 patent cited above.

The new precursor solutions have been formulated with improved stabilityand control of network formation and precipitation relative to inorganicresist materials with peroxide based ligands. Characterization ofligands as radiation sensitive in this case refers to the lability ofthe metal-ligand bond following absorption of radiation, so thatradiation can be used to induce a chemical change in the material. Inparticular, alkyl ligands stabilize the precursor solutions while alsoproviding control over the processing of the materials, and selection ofthe ratio of alkyl ligands to metal ions can be adjusted to controlproperties of the solution and the resulting coatings.

The precursor compositions comprising a mixture with different alkylligands can comprise mixtures of two alkyl-tin compounds with differentorganic ligands, three alkyl-tin compounds with different organicligands, or more than three alkyl-tin compounds with different alkylligands. Generally, for binary or tertiary mixtures, the mixturecomprises at least about 8 mole percent of each component with distinctalkyl ligands, in some embodiments at least about 12 mole percent and infurther embodiments at least about 25 mole percent of each componentwith distinct alkyl ligands. A person of ordinary skill in the art willrecognize that additional ranges of mixture components within theexplicit ranges above are contemplated and are within the presentdisclosure.

The alkyl ligands, especially branched alkyl ligands, stabilize themetal cation with respect to condensation in the absence of exposure. Inparticular, at appropriate concentrations of alkyl-based ligands,unintended formation of condensed metal oxides or metal hydroxides andrelated agglomerates are very slow if they spontaneously occur at all atroom temperature. Based on the discovery of this stabilization property,solutions can be formed with high concentrations of radiation sensitiveligands that have good shelf stability while retaining convenientprocessing to form coatings. Energy from absorbed radiation can breakthe metal-alkyl ligand bond. As these bonds are broken, thecorresponding stabilization with respect to condensation is reduced orlost, and reactive metal centers with unsaturated valence states may becreated, possibly as transient intermediates, although we do not want tobe limited by theory. The composition can further change throughreaction with atmospheric or separately supplied H₂O, formation of M-OHor through condensation to form M-O-M bonds, where M represents a metalatom. Thus, chemical changes can be controlled with radiation.Compositions with high radiation sensitive ligand concentrations can behighly stable with respect to the avoidance of unintended spontaneoushydrolysis, condensation, and agglomeration.

With respect to the oxo/hydroxo ligands for the metal ions, theseligands can be formed during processing through hydrolysis. In someembodiments, the hydrolysis can involve replacement of halide ligands ina basic aqueous solution or replacement of amido ligands (-NR₁R₂) inwater with subsequent collection of precipitated hydrolysate and/ortransfer to an organic solvent. In additional or alternativeembodiments, hydrolysable ligands may be replaced by hydroxo ligandsderived from atmospheric moisture reacting with a precursor duringcoating and baking. As described herein, low metal contaminationsynthesis approaches can be accomplished with appropriate alternativehydrolysis approaches and high-purity alkyltin precursors. Three suchapproaches are described in the examples: utilizing a water reactivealkyltin compound and obtaining water for hydrolysis from the ambientatmosphere, or addition of a controlled amount of purified water toeffectuate the hydrolysis in an organic solvent, or use of a base freefrom metal cation in concert with an alkyltin halide. One or morealternative ligands susceptible to hydrolysis by aqueous or non-aqueousacids or bases may be used in other embodiments, depending on processand synthetic considerations such as reactivity, ease of synthesis,toxicity, and other factors. In general, suitable hydrolysable ligands(X in RSnX₃) may include alkynides RC≡C, alkoxides RO⁻, azides N₃ ⁻,carboxylates RCOO⁻, halides and dialkylamides.

The through the adoption of specific synthesis procedures, the precursoralkyl tin oxide hydroxide compound can be formulated with very low metalcontamination. In particular, non-tin metals can generally be reduced tono more than 1 part per million by weight (ppm), and alkali and alkalineearth metals can be reduced to no more than about 100 parts per billionby weight (ppb). Solutions of the compounds can be correspondinglyformed. The resulting coatings can be made that provide low risk ofmetal contamination to the underlying substrate, adjacent layers,devices, and process tools. The low metal contamination can provideutility for the resist compositions for applications where certain metalcontamination is undesirable, for example, alkali metal contamination.

The processing approaches that allow for the formation of low metalcontaminant precursors avoid the use of reactants, such as bases (e.g.,NaOH), that introduce contaminant metals into the compositions.Alternative bases that can provide low metal contamination include, forexample, tetramethyl ammonium hydroxide and other quaternary ammoniumhydroxides. Also, water can be directly used for the hydrolysis in anorganic solvent with the water provided from the atmosphere or added ina controlled amount. Given the very low trace-metal levels specified insemiconductor device manufacturing (generally <10 ppb for resistcompositions), if even modest amounts of contaminant metals areintroduced, techniques have not been identified to adequately remove thecontaminant metals from a formulated alkyltin oxide hydroxide resist.Thus, appropriately hydrolysable ligands, e.g., halides or amides, arereplaced with oxo-hydroxo ligands through alternative hydrolysisreactions that do not contribute substantial concentrations of non-tinmetals. The hydrolysate can be purified to remove reaction byproductsthrough appropriate approaches, such as precipitation, washing, andrecrystallization and/or redissolving in a suitable solvent.

Generally, the precursor coating solution can comprise sufficientradiation sensitive alkyl ligands such that the solution has a molarconcentration ratio of radiation sensitive ligands to metal cations fromabout 0.1 to about 2. Ligand ratios in this range may be prepared byhydrolysis of SnX₄, RSnX₃ or R₂SnX₂ precursors in the appropriatestoichiometry, subject to the constraints of precursor stability andsolubility. The coating formed from the precursor solution is influencedby the ligand structure of the ions in the precursor solution and may bean equivalent ligand structure around the metal upon drying or theligand structure can be altered during the coating and/or dryingprocess. The coating generally is also influenced by exposure to theradiation to enable the patterning function. In general, the coating canbe represented by the formulation (R)_(z)SnO_(2−z/2−x/2)(OH).(0<(x+z)<4), where R is an alkyl group or cycloalkyl group with 3-31carbon atoms, where the alkyl or cycloalkyl group is bonded to the tinat a secondary or tertiary carbon atom. For unirradiated coating, thevalue of z can be the same or close to the coating solution value, whilethe irradiated coating generally has a lower value of z, which can bedriven close to 0 by further heating and/or irradiation, such asfollowing patterning. In particular, the alkyl ligand concentrationsprovide for a surprisingly large improvement in the precursor stabilityand control in network formation with solutions formed with organicsolvents, generally polar organic solvents. While not wanting to belimited by theory, a radiation sensitive, low polarity ligandconcentration in the appropriate range evidently reduces unintendedcondensation and agglomeration of the metal cations with correspondingoxo-ligands and/or hydroxo-ligands, to stabilize the solution. Thus, theprecursor coating solution can be stable relative to settling of solidswithout further stirring for at least one week and possibly forsignificantly longer periods of time, such as greater than a month. Dueto the long stability times, the alkyltin oxide hydroxide precursorshave increased versatility with respect to potential commercial uses.The overall molar concentration can be selected to achieve a desiredcoating thickness and desired coating properties, which can be obtainedconsistent with desired stability levels.

The polyatomic metal oxo/hydroxo cations with alkyl ligands can beselected to achieve the desired radiation absorption. In particular, tinbased coating materials exhibit good absorption of far ultraviolet lightat a 193 nm wavelength and extreme ultraviolet light at a 13.5 nmwavelength. Table 1 lists optical constants (n=index of refraction andk=extinction coefficient) at selected wavelengths for a coating materialformed from monobutyltin oxide hydrate and baked at 100° C.

TABLE 1 Wavelength (nm) n k 193 1.75 0.211 248 1.79 0.0389 365 1.63 0405 1.62 0 436 1.61 0

To correspondingly provide a high absorption of radiation generally usedfor patterning, it is desirable to include Sn, In and Sb metals in theprecursor solutions, although these metals can be combined with othermetals to adjust the properties, especially the radiation absorption. Hfprovides good absorption of electron beam material and extreme UVradiation and In and Sb provide strong absorption of extreme ultravioletlight at 13.5 nm. For example, one or more metal compositions comprisingTi, V, Mo, or W or combinations thereof can be added to the precursorsolution to form a coating material with an absorption edge moved tolonger wavelengths, to provide, for example, sensitivity to 248 nmwavelength ultraviolet light. These other metal ions may or may notinvolve an alkyl ligand, and suitable salts for the metal ions withoutalkyl ligands for use in the precursor compositions described herein mayinclude, for example, organic or inorganic salts, amides, alkoxides, orthe like that are soluble in the solvent for the coating precursorsolution. For the determination of metal contaminants, clearlyspecifically added functional metals are not considered as contaminants,and these metals can generally be identified by a presence in theprecursor solutions at a level greater than 100 ppm by weight, and suchmetals can be selected to avoid undesirable contamination for aparticular application.

In general, the desired hydrolysate can be dissolved in an organicsolvent, e.g., alcohols, esters or combinations thereof to form theprecursor solution. The concentrations of the species in the coatingsolutions can be selected to achieve desired physical properties of thesolution. In particular, lower concentrations overall can result indesirable properties of the solution for certain coating approaches,such as spin coating, that can achieve thinner coatings using reasonablecoating parameters. It can be desirable to use thinner coatings toachieve ultrafine patterning as well as to reduce material costs. Ingeneral, the concentration can be selected to be appropriate for theselected coating approach. Coating properties are described furtherbelow.

The precursor solutions can be deposited generally with any reasonablecoating or printing technique as described further below. The coatinggenerally is dried, and heat can be applied to stabilize or partiallycondense the coating prior to irradiation. Generally, the coatings arethin, such as with an average thickness of less than 10 microns, andvery thin submicron coatings, for example, no more than about 100nanometers (nm), can be desirable to pattern very small features. Toform high resolution patterns, radiation sensitive organic compositionscan be used to introduce patterns, and the compositions can be referredto as resists since portions of the composition are processed to beresistant to development/etching such that selective material removalcan be used to introduce a selected pattern. The dried coating can besubjected to appropriate radiation, e.g., extreme ultraviolet light,e-beam or ultraviolet light, with the selected pattern or the negativeof the pattern to form a latent image with developer resistant regionsand developer dissolvable regions. After exposure to appropriateradiation, and prior to developing, the coating can be heated orotherwise reacted to further differentiate the latent image fromnon-irradiated areas. The latent image is contacted with the developerto form a physical image, i.e. a patterned coating. The patternedcoating can be further heated to stabilize the remaining coatingpatterned on the surface. The patterned coating can be used as aphysical mask to perform further processing, e.g., etching of thesubstrate and/or deposition of additional materials according to thepattern. At appropriate points of the processing after using thepatterned resist as desired, the remaining patterned coating can beremoved, although the patterned coating can be incorporated into theultimate structure. Very fine features can be accomplished effectivelywith the patterning compositions described herein.

In some embodiments, the resulting patterned material can beincorporated into the structure following appropriate stabilizationthrough at least some condensation into an inorganic metal oxidematerial, as a component of ultimate device(s). If the patternedinorganic coating material is incorporated into the structure, forexample as a stable dielectric layer, many steps of the processingprocedure can be eliminated through the use of a direct patterning ofthe material with radiation. In general, it has been found that veryhigh resolution structures can be formed using thin inorganic coatingmaterials exposed using short wavelength electromagnetic radiationand/or electron beams, and that line-width roughness can be reduced tovery low levels for the formation of improved patterned structures.

Refined precursor solutions with greater stability also provide for acoating material having the potential of a greater development ratecontrast between the radiation exposed and unexposed portions of thesubstrate, which surprisingly can be achieved simultaneously with eitherpositive tone patterning or negative tone patterning. Specifically, theirradiated coating material or the un-irradiated coating material can berelatively more easily dissolved by suitable developer compositions.Thus, with the improved compositions and corresponding materials,positive- or negative-tone imaging can be achieved through choice ofdeveloper. At the same time, the pitch can be made very small betweenadjacent elements with appropriate isolation, generally electricalisolation, between the adjacent elements. The irradiated coatingcomposition can be very sensitive to a subsequent development/etchingprocess so that the coating composition can be made very thin withoutcompromising the efficacy of the development process with respect toselective and clean removal of the coating composition while leavingappropriate portions of the irradiated patterning composition on thesurface of the substrate. The ability to shorten the exposure time tothe developer further is consistent with the use of thin coatingswithout damaging the patterned portions of the coating.

The formation of integrated electronic devices and the like generallyinvolves the patterning of the materials to form individual elements orcomponents within the structures. This patterning can involve differentcompositions covering selected portions of stacked layers that interfacewith each other vertically and/or horizontally to induce desiredfunctionality. The various materials can comprise semiconductors, whichcan have selected dopants, dielectrics, electrical conductors and/orother types of materials. The radiation sensitive organometalliccompositions described herein can be used for the direct formation ofdesired inorganic material structures within the device and/or as aradiation patternable inorganic resist that is a replacement for anorganic resist. In either case, significant processing improvements canbe exploited, and the structure of the patterned material can be alsoimproved.

Precursor Solutions

The precursor solutions for forming the resist coatings generallycomprise tin cations with appropriate alkyl stabilizing ligands in asolvent, generally an organic solvent. The precursor solutions and theultimate resist coatings are based on metal oxide chemistry, and theorganic solutions of metal polycations with alkyl ligands provide stablesolutions with good resist properties. Branched alkyl ligands inparticular provide improved patterning capability. The ligands providethe radiation sensitivity, and the particular selection of ligands caninfluence the radiation sensitivity. Also, the precursor solutions canbe designed to achieve desired levels of radiation absorption for aselected radiation based on the selection of the metal cations as wellas the associated ligands. The concentration of ligand stabilized metalcations in the solution can be selected to provide suitable solutionproperties for a particular deposition approach, such as spin coating.The precursor solutions have been formulated to achieve very high levelsof stability such that the precursor solutions have appropriate shelflives for commercial products. As described in the following section,the precursor solutions can be applied to a substrate surface, dried andfurther processed to form an effective radiation resist. The precursorsolutions are designed to form a coating composition upon at leastpartial solvent removal and ultimately an inorganic solid dominated bytin oxides upon irradiation and/or thermal treatment, exposure to aplasma, or similar processing.

The precursor solutions generally comprise one or more tin cations. Inaqueous solutions, metal cations are hydrated due to interactions withthe water molecules, and hydrolysis can take place to bond oxygen atomsto the metal ion to form hydroxide ligands or oxo bonds with thecorresponding release of hydrogen ions. The nature of the interactionsis generally pH dependent. As additional hydrolysis takes place inaqueous solutions, the solutions can become unstable with respect toprecipitation of the metal oxide or with respect to gelation.Ultimately, it is desirable to form the oxide material, but thisprogression can be controlled better with the precursor solutions basedon organic solvents with alkyl ligand stabilized metal cations. Ifplaced over an atmosphere with water vapor, the solvent may comprisesome dissolved water in equilibrium with the partial pressure of waterin contact with the solvent, and the examples demonstrate the use ofdissolved water to effect controlled hydrolysis of hydrolysable ligands.With the precursor solutions based on alkyl-stabilization ligands and anorganic solvent, Progression to the oxide can be controlled as part ofthe procedure for processing the solution first to a coating materialand then to the ultimate metal oxide composition with organic ligands.As described herein, alkyl ligands, especially branched alkyl ligandsand/or combinations of alkyl ligands, can be used to provide significantcontrol to the processing of the solution to an effective radiationresist composition.

In general, the precursor compounds can be represented by the formulaRSnO_((3/2−x/2))(OH)_(x), (0<x<3) where R is a linear or branched (i.e.,secondary or tertiary at the metal bonded carbon atom) alkyl group. Rgenerally has from 1 to 31 carbon atoms with 3 to 31 carbon atoms forthe branched embodiments. In particular, branched alkyl ligands aredesirable where the compound can be represented in anotherrepresentation by R₁R₂R₃CSnO_((3/2−x/2))(OH)_(x), (0<x<3) where R₁ andR₂ are independently an alkyl group with 1-10 carbon atoms, and R₃ ishydrogen or an alkyl group with 1-10 carbon atoms. In some embodimentsR₁ and R₂ can form a cyclic alkyl moiety, and R₃ may also join the othergroups in a cyclic moiety. Precursor solutions may also comprise blendsof compositions with different alkyl ligands Exemplified branched alkylligands include isopropyl (R₁ and R₂ are methyl and R₃ is hydrogen),tert-butyl (R₁, R₂ and R₃ are methyl), sec-butyl (R₁ is methyl, R₂ is—CHCH₃, and R₃ is hydrogen) and tert-amyl (R₁ and R₂ are methyl and R₃is —CHCH₃). Preliminary experiments with cyclic alkyl ligands have shownpromising results. Examples of suitable cyclic groups include, forexample, 1-adamantyl (—C(CH₂)₃(CH)₃(CH₂)₃ or tricyclo(3.3.1.13,7) decanebonded to the metal at tertiary carbon) and 2-adamantyl(—CH(CH)₂(CH₂)₄(CH)₂(CH₂) or tricyclo(3.3.1.13,7) decane bonded to themetal at a secondary carbon). Thus, the solutions of the metal cationsare poised for further processing. In particular, it can be desirous touse as an added component of the precursor solution, a polynuclear tinoxo/hydroxo cation that can poise the solution further toward a tinoxide composition. In general, the precursor solution comprises fromabout 0.01M to about 1.4M metal polynuclear oxo/hydroxo cation, infurther embodiments from about 0.05M to about 1.2M, and in additionalembodiments from about 0.1M to about 1.0M. A person of ordinary skill inthe art will recognize that additional ranges of tin polynuclearoxo/hydroxo cations within the explicit ranges above are contemplatedand are within the present disclosure.

The precursor compositions comprising a mixture with different organicligands can comprise mixtures of two alkyl-tin compounds with differentalkyl ligands, three alkyl-tin compounds with different alkyl ligands,or more than three alkyl-tin compounds with different alkyl ligands.Generally, for binary or tertiary mixtures, the mixture comprises atleast about 8 mole percent of each component with distinct allylligands, in some embodiments at least about 12 mole percent and infurther embodiments at least about 25 mole percent of each componentwith distinct alkyl ligands. A person of ordinary skill in the art willrecognize that additional ranges of mixture components within theexplicit ranges above are contemplated and are within the presentdisclosure.

The metal generally significantly influences the absorption ofradiation. Tin provides strong absorption of extreme ultraviolet lightat 13.5 nm. In combination with alkyl ligands, the cations also providegood absorption of ultraviolet light at 193 nm wavelength. Tin alsoprovides good absorption of electron beam radiation. The energy absorbedis modulated by the metal-organic interactions, which can result in therupturing of the metal-ligand and the desired control over the materialproperties.

The alkyl ligands stabilize the composition with respect to unintendedspontaneous condensation and agglomeration of the hydrolysate. Inparticular, at high relative concentration of alkyl ligands, formationof condensed metal oxides or metal hydroxides are very slow if thecondensation spontaneously occurs at all at room temperature. Based onthe discovery of this stabilization property, hydrolysate solutions canbe formed with high concentrations of radiation sensitive ligands thathave good shelf stability while retaining convenient processing to formcoatings. Radiation sensitive ligands include alkyl moieties forming atin-carbon bond. Energy from absorbed radiation can break the tin-alkylligand bond. As these bonds are broken, the corresponding stabilizationwith respect to condensation is reduced or lost. The composition canchange through formation of M-OH or through condensation to form M-O-Mbonds, where M represents a metal atom. Thus, chemical changes can becontrolled with radiation. Compositions with high radiation sensitiveligand concentrations can be highly stable with respect to the avoidanceof spontaneous formation of hydroxide and condensation.

Some suitable metal compositions with desired ligand structures can bepurchased from commercial sources, such as Alfa Aesar (MA, USA) and TCIAmerica (OR, USA), see Examples below, and other metal-ligandcompositions can be synthesized as described below. Low metalcontaminant precursor compositions are synthesized using the methodsdescribed herein.

In general, alkyl ligands can be, for example, methyl, ethyl, propyl,butyl, and branched alkyl. Suitable branched alkyl ligands can be, forexample, isopropyl, tert-butyl, tert-amyl, 2-butyl, cyclohexyl,cyclopentyl, cyclobutyl, cyclopropyl, 1-adamantyl or 2-adamantyl.Improved patterning results have been obtained using branched alkylligands. But fuller advantage of ligand selection has been achievedthrough the use of mixed alkyl ligands, as separately advantageouspatterning properties such as dose and line-width-roughness imparted bydifferent ligands may be obtained through the teachings herein throughblending of multiple alkyl ligands as illustrated in the examplesprovided.

It has been found that the radiation curing doses can scaleapproximately linearly for mixtures of precursor compounds withdifferent alkyl ligands based on the radiation doses for the respectiveindividual precursor compounds. Due to the lower radiation doses thatcan be used with the branched alkyl ligands, it is generally desirablefor the mixtures to comprise at least one branched organic ligand. Butcorrespondingly it has been discovered that the line width roughness canbe improved with mixtures of precursor compounds with different organicligands. While not wanting to be limited by theory, it is possible thatthe improved line width roughness values observed for the mixturecompositions may be due to facilitated etchings for the mixturecompositions without significantly diminishing the contrast in thepattern. In this context, the observations may extend to mixturecompositions containing combinations of organo-tin compounds bearingbranched or unbranched alkyls.

As described herein, processing approaches have been developed thatprovide for reduction of metal contamination. Thus, the precursorsolutions can be formulated that have very low levels of non-tin metal.In general, the non-tin metal concentrations can all be individuallyreduced to values of no more than about 1 part per million by weight(ppm) in further embodiments, no more than about 200 parts per billionby weight (ppb), in additional embodiments no more than about 50 ppb,and in other embodiments no more than about 10 ppb. In some embodiments,it may be desirable to add other metal elements to influence processing,and generally these can be identified by levels of at least about 1weight percent and in some embodiments at least about 2 weight percent,and can thus be distinguished from contaminant metals, if appropriate.Metal contaminants to be decreased in particular include alkali metalsand alkaline earth metals, Au, Ag, Cu, Fe, Pd, Pt, Co, Mn, and Ni. Aperson or ordinary skill in the art will recognize that additionalranges of metal levels within the explicit levels above are contemplatedand are within the present disclosure.

Processing to form the organotin oxide hydroxide compositions haspreviously involved use of reactants that introduce significant non-tinmetal contaminants, such as sodium from sodium hydroxide base. Thealternative synthesis methods described herein can be used for preparinghydrolysates with linear or branched alkyl ligands, including compoundsnot known to be commercially available as well as correspondingcommercially available compounds that may have metal contaminants. Waysto remove the sodium to a sufficiently low level have not been found, soalternative synthesis techniques have been developed. Thus, alternativeprocesses have been developed that allow for the significant reductionof metal contamination. In particular, high-purity water-reactiveprecursor compounds that do not require added base to form an organotinhydrolysate may be used. Hydrolysate syntheses can be performed in anon-aqueous solvent or with an aqueous solvent where the productcompounds immediately precipitate. In some embodiments, water can beintroduced in just a sufficient amount to hydrolyse the hydrolysableligands to form the desired alkyl tin oxide hydroxide compound.

With respect to the oxo/hydroxo ligands for the metal ions, theseligands can be formed during processing through hydrolysis. In someembodiments, the hydrolysis can involve replacement of hydrolysableligands to form oxo (O) and/or hydroxo (—OH) ligands. For example,halide ligands can be hydrolysed in a basic aqueous solution withsubsequent transfer to an organic solvent. However, for the productionof precursor compositions with low metal contamination, performing thehydrolysis using alternative reactions has been found to be desirable.Specific examples are presented below.

In some embodiments, a composition comprising the tin ions with organicstabilizing ligands and hydrolysable ligands are dissolved in an organicsolvent, which is then contacted with a basic aqueous solution,whereupon substitution of the hydrolysable ligands with hydroxo ligandsmay occur. After providing enough time to form hydroxo ligands, theaqueous solution can be separated from the organic phase assuming thatthe organic liquid is not soluble in the aqueous liquid. In someembodiments, the oxo/hydroxo ligands can be formed through hydrolysisfrom atmospheric water. The hydrolysable metal ion composition can beheated in the presence of atmospheric moisture so that the oxo/hydroxoligands form directly in the coating material, which can be relativelyfacile due to the high surface area. An example of hydrolysis fromatmospheric water is also described below. In additional or alternativeembodiments, sufficient water to effectuate the hydrolysis is dissolvedinto an organic solvent along with the precursor compound with thehydrolysable ligands.

To form the precursor compound with the alkyl ligands and hydrolysableligands, M-C bonds can also be formed in a solution phase substitutionreaction. The following reactions are representative suitable reactionsfor the substitution reactions to form Sn—C bonds:n RCl+Sn→R_(n)SnCl_(4−n)+Residual4 RMgBr+SnCl₄→R₄Sn+4 MgBrCl3 SnCl₄+4R₃Al→3 R₄Sn+4 AlCl₃R₄Sn+SnCl₄→2 R₂SnCl₂where R represents an alky ligand. Generally, different suitable halidescan be substituted in the above reactions. The reactions can be carriedout in a suitable organic solvent in which the reactants have reasonablesolubility.

With respect to methods for forming low metal contaminant precursorsolutions, reactants are chosen to avoid introduction of metalcontaminants during the hydrolysis reactions to form the tin oxidehydroxide compounds from the alkyl tin compounds with hydrolysablegroups. Two general approaches are used successfully in the examples. Insome embodiments, the hydrolysis is performed with the precursorcompounds in an organic solvent and sufficient water to effectuate thehydrolysis is introduced. The sufficient water to complete thehydrolysis of the hydrolysable ligands can be introduced from theambient water vapor or injected into the organic solvent and mixed.Alternatively, the hydrolysis can be performed in water in whichcatalytic base is introduced in a form that does not introduce metalcontaminants. For example, in the examples, aqueous tetramethylammoniumhydroxide (TMAH) is used, which is available commercially with low metalcontamination due to use in the semiconductor industry. Hydrolysableligands can be selected appropriately for the specific approach used forthe hydrolysis reaction as described in the examples.

In general, the desired hydolysate compounds can be dissolved in anorganic solvent, e.g., alcohols, esters or combinations thereof. Inparticular, suitable solvents include, for example, aromatic compounds(e.g., xylenes, toluene), ethers (anisole, tetrahydrofuran), esters(propylene glycol monomethyl ether acetate, ethyl acetate, ethyllactate), alcohols (e.g., 4-methyl-2-propanol, 1-butanol, methanol,isopropyl alcohol, 1-propanol,), ketones (e.g., methyl ethyl ketone),mixtures thereof, and the like. In general, organic solvent selectioncan be influenced by solubility parameters, volatility, flammability,toxicity, viscosity and potential chemical interactions with otherprocessing materials. After the components of the solution are dissolvedand combined, the character of the species may change as a result ofpartial hydration and condensation, especially during the coatingprocess. When the composition of the solution is referenced herein, thereference is to the components as added to the solution, since complexformulations may produce metal polynuclear species in solution that maynot be well characterized. For certain applications it is desirable forthe organic solvent to have a flash point of no less than about 10° C.,in further embodiments no less than about 20° C. and in furtherembodiment no less than about 25° C. and a vapor pressure at 20° C. ofno more than about 10 kPa, in some embodiments no more than about 8 kPaand in further embodiments no more than about 6 kPa. A person ofordinary skill in the art will recognize that additional ranges of flashpoint and vapor pressure within the explicit ranges above arecontemplated and are within the present disclosure.

In general, precursor solutions are well mixed using appropriate mixingapparatuses suitable for the volume of material being formed. Suitablefiltration can be used to remove any contaminants or other componentsthat do not appropriately dissolve. In some embodiments, it may bedesirable to form separate solutions that can be combined to form theprecursor solution from the combination. Specifically, separatesolutions can be formed comprising one or more of the following: themetal polynuclear oxo/hydroxo cations, any additional metal cations, andthe organic ligands. If multiple metal cations are introduced, themultiple metal cations can be introduced into the same solution and/orin separate solutions. Generally, the separate solutions or the combinedsolutions can be well mixed. In some embodiments, the metal cationsolution is then mixed with the organic-based ligand solution such thatthe organic-based ligand can conjugate with the metal cations. Theresulting solution can be referred to as a stabilized metal cationsolution. In some embodiments, the stabilized metal cation solution isallowed to react for a suitable period of time to provide for stableligand formation, which may or may not also involve cluster formation insolution, whether or not mixed metal ions are introduced. In someembodiments, the reaction or stabilization time for the solution can befor at least about five minutes, in other embodiments at least about 1hour, and in further embodiments from about 2 hours to about 48 hoursprior to further processing. A person of ordinary skill in the art willrecognize that additional ranges of stabilization periods arecontemplated and are within the present disclosure.

The concentrations of the species in the precursor solutions can beselected to achieve desired physical properties of the solution. Inparticular, lower concentrations overall can result in desirableproperties of the solution for certain coating approaches, such as spincoating, that can achieve thinner coatings using reasonable coatingparameters. It can be desirable to use thinner coatings to achieveultrafine patterning as well as to reduce material costs. In general,the concentration can be selected to be appropriate for the selectedcoating approach. Coating properties are described further below.

Stability of the precursor solutions can be evaluated with respect tochanges relative to the initial solution. Specifically, a solution haslost stability if phase separation occurs with the production of largesol particles or if the solution loses its ability to perform desiredpattern formation. Based on the improved stabilization approachesdescribed herein, the solutions can be stable for at least about a weekwithout additional mixing, in further embodiments at least about 2weeks, in other embodiments at least about 4 weeks. A person of ordinaryskill in the art will recognize that additional ranges of stabilizationtimes are contemplated and are within the present disclosure. Thesolutions can be formulated with sufficient stabilization times that thesolutions can be commercially distributed with appropriate shelf lives.

Coating Material

A coating material is formed through the deposition and subsequentprocessing of the precursor solution onto a selected substrate. Asubstrate generally presents a surface onto which the coating materialcan be deposited, and the substrate may comprise a plurality of layersin which the surface relates to an upper most layer. In someembodiments, the substrate surface can be treated to prepare the surfacefor adhesion of the coating material. Also, the surface can be cleanedand/or smoothed as appropriate. Suitable substrate surfaces can compriseany reasonable material. Some substrates of particular interest include,for example, silicon wafers, silica substrates, other inorganicmaterials such as ceramic materials, polymer substrates, such as organicpolymers, composites thereof and combinations thereof across a surfaceand/or in layers of the substrate. Wafers, such as relatively thincylindrical structures, can be convenient, although any reasonableshaped structure can be used. Polymer substrates or substrates withpolymer layers on non-polymer structures can be desirable for certainapplications based on their low cost and flexibility, and suitablepolymers can be selected based on the relatively low processingtemperatures that can be used for the processing of the patternablematerials described herein. Suitable polymers can include, for example,polycarbonates, polyimides, polyesters, polyalkenes, copolymers thereofand mixtures thereof. In general, it is desirable for the substrate tohave a flat surface, especially for high resolution applications.However, in specific embodiments the substrate may possess substantialtopography, where the resist coating is intended to fill or planarizefeatures for particular patterning applications. Such a function of theresist material is described in published U.S. patent application2015/0253667A1 to Bristol et al., entitled “Pre-Patterned Hard Mask forUltrafast Lithographic Imaging,” incorporated herein by reference.

In general, any suitable coating process can be used to deliver theprecursor solution to a substrate. Suitable coating approaches caninclude, for example, spin coating, spray coating, dip coating, knifeedge coating, printing approaches, such as inkjet printing and screenprinting, and the like. Some of these coating approaches form patternsof coating material during the coating process, although the resolutionavailable currently from printing or the like has a significantly lowerlevel of resolution than available from radiation based patterning asdescribed herein. The coating material can be applied in multiplecoating steps to provide greater control over the coating process. Forexample, multiple spin coatings can be performed to yield an ultimatecoating thickness desired. The heat processing described below can beapplied after each coating step or after a plurality of coating steps.

If patterning is performed using radiation, spin coating can be adesirable approach to cover the substrate relatively uniformly, althoughthere can be edge effects. In some embodiments, a wafer can be spun atrates from about 500 rpm to about 10,000 rpm, in further embodimentsfrom about 1000 rpm to about 7500 rpm and in additional embodiments fromabout 2000 rpm to about 6000 rpm. The spinning speed can be adjusted toobtain a desired coating thickness. The spin coating can be performedfor times from about 5 seconds to about 5 minutes and in furtherembodiments from about 15 seconds to about 2 minutes. An initial lowspeed spin, e.g. at 50 rpm to 250 rpm, can be used to perform an initialbulk spreading of the composition across the substrate. A back siderinse, edge bead removal step or the like can be performed with water orother suitable solvent to remove any edge bead. A person or ordinaryskill in the art will recognize that additional ranges of spin coatingparameters within the explicit ranges above are contemplated and arewithin the present disclosure.

The thickness of the coating generally can be a function of theprecursor solution concentration, viscosity and the spin speed for spincoating. For other coating processes, the thickness can generally alsobe adjusted through the selection of the coating parameters. In someembodiments, it can be desirable to use a thin coating to facilitateformation of small and highly resolved features in the subsequentpatterning process. For example, the coating materials after drying canhave an average thickness of no more than about 10 microns, in otherembodiments no more than about 1 micron, in further embodiments no morethan about 250 nanometers (nm), in additional embodiments from about 1nanometers (nm) to about 50 nm, in other embodiments from about 2 nm toabout 40 nm and in some embodiments from about 3 nm to about 25 nm. Aperson of ordinary skill in the art will recognize that additionalranges of thicknesses within the explicit ranges above are contemplatedand are within the present disclosure. The thickness can be evaluatedusing non-contact methods of x-ray reflectivity and/or ellipsometrybased on the optical properties of the film. In general, the coatingsare relatively uniform to facilitate processing. In some embodiments,the variation in thickness of the coating varies by no more than ±50%from the average coating thickness, in further embodiments no more than±40% and in additional embodiments no more than about ±25% relative tothe average coating thickness. In some embodiments, such as highuniformity coatings on larger substrates, the evaluation of coatinguniformity may be evaluated with a 1 centimeter edge exclusion, i.e.,the coating uniformity is not evaluated for portions of the coatingwithin 1 centimeter of the edge. A person of ordinary skill in the artwill recognize that additional ranges within the explicit ranges aboveare contemplated and are within the present disclosure.

The coating process itself can result in the evaporation of a portion ofthe solvent since many coating processes form droplets or other forms ofthe coating material with larger surface areas and/or movement of thesolution that stimulates evaporation. The loss of solvent tends toincrease the viscosity of the coating material as the concentration ofthe species in the material increases. An objective during the coatingprocess can be to remove sufficient solvent to stabilize the coatingmaterial for further processing. These species may condense duringcoating or subsequent heating to forming a hydrolysate coating material.In general, the coating material can be heated prior to radiationexposure to further drive off solvent and promote densification of thecoating material. The dried coating material may generally form apolymeric metal oxo/hydroxo network based on the oxo-hydroxo ligands tothe metals in which the metals also have some alkyl ligands, or amolecular solid comprised of polynuclear metal oxo/hydroxo species withalkyl ligands.

The solvent removal process may or may not be quantitatively controlledwith respect to specific amounts of solvent remaining in the coatingmaterial, and empirical evaluation of the resulting coating materialproperties generally can be performed to select processing conditionsthat are effective for the patterning process. While heating is notneeded for successful application of the process, it can be desirable toheat the coated substrate to speed the processing and/or to increase thereproducibility of the process. In embodiments in which heat is appliedto remove solvent, the coating material can be heated to temperaturesfrom about 45° C. to about 250° C. and in further embodiments from about55° C. to about 225° C. The heating for solvent removal can generally beperformed for at least about 0.1 minute, in further embodiments fromabout 0.5 minutes to about 30 minutes and in additional embodiments fromabout 0.75 minutes to about 10 minutes. A person of ordinary skill inthe art will recognize that additional ranges of heating temperature andtimes within the explicit ranges above are contemplated and are withinthe present disclosure. As a result of the heat treatment anddensification of the coating material, the coating material can exhibitan increase in index of refraction and in absorption of radiationwithout significant loss of contrast.

Patterned Exposure and Patterned Coating Material

The coating material can be finely patterned using radiation. As notedabove, the composition of the precursor solution and thereby thecorresponding coating material can be designed for sufficient absorptionof a desired form of radiation. The absorption of the radiation resultsin energy that can break the bonds between the metal and alkyl ligandsso that at least some of the alkyl ligands are no longer available tostabilize the material. Radiolysis products, including alkyl ligands orfragments may diffuse out of the film, or not, depending on processvariables and the identity of such products. With the absorption of asufficient amount of radiation, the exposed coating material condenses,i.e. forms an enhanced metal oxo/hydroxo network, which may involvewater absorbed from the ambient atmosphere. The radiation generally canbe delivered according to a selected pattern. The radiation pattern istransferred to a corresponding pattern or latent image in the coatingmaterial with irradiated areas and un-irradiated areas. The irradiatedareas comprise chemically altered coating material, and theun-irradiated areas comprise generally the as-formed coating material.As noted below, very sharp edges can be formed upon development of thecoating material with the removal of the un-irradiated coating materialor alternatively with selective removal of the irradiated coatingmaterial.

Radiation generally can be directed to the coated substrate through amask or a radiation beam can be controllably scanned across thesubstrate. In general, the radiation can comprise electromagneticradiation, an electron beam (beta radiation), or other suitableradiation. In general, electromagnetic radiation can have a desiredwavelength or range of wavelengths, such as visible radiation,ultraviolet radiation or x-ray radiation. The resolution achievable forthe radiation pattern is generally dependent on the radiationwavelength, and a higher resolution pattern generally can be achievedwith shorter wavelength radiation. Thus, it can be desirable to useultraviolet light, x-ray radiation or an electron beam to achieveparticularly high resolution patterns.

Following International Standard ISO 21348 (2007) incorporated herein byreference, ultraviolet light extends between wavelengths of greater thanor equal 100 nm and less than 400 nm. A krypton fluoride laser can beused as a source for 248 nm ultraviolet light. The ultraviolet range canbe subdivided in several ways under accepted Standards, such as extremeultraviolet (EUV) from greater than or equal 10 nm to less than 121 nmand far ultraviolet (FUV) from greater than or equal to 122 nm to lessthan 200 nm A 193 nm line from an argon fluoride laser can be used as aradiation source in the FUV. EUV light has been used for lithography at13.5 nm, and this light is generated from a Xe or Sn plasma sourceexcited using high energy lasers or discharge pulses. Soft x-rays can bedefined from greater than or equal 0.1 nm to less than 10 nm.

The amount of electromagnetic radiation can be characterized by afluence or dose which is obtained by the integrated radiative flux overthe exposure time. Suitable radiation fluences can be from about 1mJ/cm² to about 150 mJ/cm², in further embodiments from about 2 mJ/cm²to about 100 mJ/cm², and in further embodiments from about 3 mJ/cm² toabout 50 mJ/cm². A person of ordinary skill in the art will recognizethat additional ranges of radiation fluences within the explicit rangesabove are contemplated and are within the present disclosure.

With electron beam lithography, the electron beam generally inducessecondary electrons which generally modify the irradiated material. Theresolution can be a function at least in part of the range of thesecondary electrons in the material in which a higher resolution isgenerally believed to result from a shorter range of the secondaryelectrons. Based on high resolution achievable with electron lithographyusing the inorganic coating materials described herein, the range of thesecondary electrons in the inorganic material is limited. Electron beamscan be characterized by the energy of the beam, and suitable energiescan range from about 5 V to about 200 kV (kilovolt) and in furtherembodiments from about 7.5 V to about 100 kV. Proximity-corrected beamdoses at 30 kV can range from about 0.1 microcoulombs per centimetersquared to about 5 millicoulombs per centimeter squared (mC/cm²), infurther embodiments from about 0.5 μC/cm² to about 1 mC/cm² and in otherembodiments from about 1 μC/cm² to about 100 μC/cm². A person ofordinary skill in the art can compute corresponding doses at other beamenergies based on the teachings herein and will recognize thatadditional ranges of electron beam properties within the explicit rangesabove are contemplated and are within the present disclosure.

Based on the design of the coating material, there is a large contrastof material properties between the irradiated regions that havecondensed coating material and the un-irradiated, coating material withsubstantially intact organic ligands. It has been found that thecontrast at a given dose can be improved with a post-irradiation heattreatment, although satisfactory results can be achieved in someembodiments without post-irradiation heat treatment. The post-exposureheat treatment seems to anneal the irradiated coating material toincrease its condensation without significantly condensing theun-irradiated regions of coating material based on thermal breaking ofthe organic ligand-metal bonds. For embodiments in which a postirradiation heat treatment is used, the post-irradiation heat treatmentcan be performed at temperatures from about 45° C. to about 250° C., inadditional embodiments from about 50° C. to about 190° C. and in furtherembodiments from about 60° C. to about 175° C. The post exposure heatingcan generally be performed for at least about 0.1 minute, in furtherembodiments from about 0.5 minutes to about 30 minutes and in additionalembodiments from about 0.75 minutes to about 10 minutes. A person ofordinary skill in the art will recognize that additional ranges ofpost-irradiation heating temperature and times within the explicitranges above are contemplated and are within the present disclosure.This high contrast in material properties further facilitates theformation of sharp lines in the pattern following development asdescribed in the following section.

Following exposure with radiation, the coating material is patternedwith irradiated regions and un-irradiated regions. Referring to FIGS. 1and 2, a patterned structure 100 is shown comprising a substrate 102, athin film 103 and patterned coating material 104. Patterned coatingmaterial 104 comprises regions 110, 112, 114, 116 of irradiated coatingmaterial and uncondensed regions 118, 120, 122 of un-irradiated coatingmaterial. The pattern formed by condensed regions 110, 112, 114, 116 anduncondensed regions 118, 120, 122 represent a latent image into thecoating material, and the development of the latent image is discussedin the following section.

Development and Patterned Structure

Development of the image involves the contact of the patterned coatingmaterial including the latent image to a developer composition to removeeither the un-irradiated coating material to form the negative image orthe irradiated coating to form the positive image. Using the resistmaterials described herein, effective negative patterning or positivepatterning can be performed with desirable resolution using appropriatedeveloping solutions, generally based on the same coating. Inparticular, the irradiated regions are at least partially condensed toincrease the metal oxide character so that the irradiated material isresistant to dissolving by organic solvents while the un-irradiatedcompositions remain soluble in the organic solvents. Reference to acondensed coating material refers to at least partial condensation inthe sense of increasing the oxide character of the material relative toan initial material. On the other hand, the un-irradiated material isless soluble in weak aqueous bases or acids due to the hydrophobicnature of the material so that aqueous bases can be used to remove theirradiated material while maintaining the non-irradiated material forpositive patterning.

The coating compositions with organic-stabilization ligands produce amaterial that is inherently relatively hydrophobic. Irradiation to breakat least some of the organic metal bonds converts the material into aless hydrophobic, i.e., more hydrophilic, material. This change incharacter provides for a significant contrast between the irradiatedcoating and non-irradiated coating that provides for the ability to doboth positive tone patterning and negative tone patterning with the sameresist composition. Specifically, the irradiated coating materialcondenses to some degree into a more of a metal oxide composition;however, the degree of condensation generally is moderate withoutsignificant heating so that the irradiated material is relativelystraightforward to develop with convenient developing agents.

With respect to negative tone imaging, referring to FIGS. 3 and 4, thelatent image of the structure shown in FIGS. 1 and 2 has been developedthrough contact with a developer to form patterned structure 130. Afterdevelopment of the image, substrate 102 is exposed along the top surfacethrough openings 132, 134, 135. Openings 132, 134, 135 are located atthe positions of uncondensed regions 118, 120, 122 respectively. Withrespect to positive tone imaging, referring to FIGS. 5 and 6, the latentimage of the structure shown in FIGS. 1 and 2 has been developed to formpatterned structure 140. Patterned structure 140 has the conjugate imageof patterned structure 130. Patterned structure 140 has substrate 102exposed at positions of irradiated regions 110, 112, 114, 116 that aredeveloped to form openings 142, 144, 146, 148.

For the negative tone imaging, the developer can be an organic solvent,such as the solvents used to form the precursor solutions. In general,developer selection can be influenced by solubility parameters withrespect to the coating material, both irradiated and non-irradiated, aswell as developer volatility, flammability, toxicity, viscosity andpotential chemical interactions with other process material. Inparticular, suitable developers include, for example, aromatic compounds(e.g., benzene, xylenes, toluene), esters (e.g., propylene glycolmonomethyl ester acetate, ethyl acetate, ethyl lactate, n-butyl acetate,butyrolactone), alcohols (e.g., 4-methyl-2-pentanol, 1-butanol,isopropanol, 1-propanol, methanol), ketones (e.g., methyl ethyl ketone,acetone, cyclohexanone, 2-heptanone, 2-octanone), ethers (e.g.,tetrahydrofuran, dioxane, anisole) and the like. The development can beperformed for about 5 seconds to about 30 minutes, in furtherembodiments from about 8 seconds to about 15 minutes and in additionembodiments from about 10 seconds to about 10 minutes. A person ofordinary skill in the art will recognize that additional ranges withinthe explicit ranges above are contemplated and are within the presentdisclosure.

For positive tone imaging, the developer generally can be aqueous acidsor bases. In some embodiments, aqueous bases can be used to obtainsharper images. To reduce contamination from the developer, it can bedesirable to use a developer that does not have metal atoms. Thus,quaternary ammonium hydroxide compositions, such as tetraethylammoniumhydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxideor combinations thereof, are desirable as developers. In general, thequaternary ammonium hydroxides of particular interest can be representedwith the formula R₄NOH, where R=a methyl group, an ethyl group, a propylgroup, a butyl group, or combinations thereof. The coating materialsdescribed herein generally can be developed with the same developercommonly used presently for polymer resists, specifically tetramethylammonium hydroxide (TMAH). Commercial TMAH is available at 2.38 weightpercent, and this concentration can be used for the processing describedherein. Furthermore, mixed quaternary tetraalkyl-ammonium hydroxides canbe used. In general, the developer can comprise from about 0.5 to about30 weight percent, in further embodiments from about 1 to about 25weight percent and in other embodiments from about 1.25 to about 20weight percent tetra-alkylammonium hydroxide or similar quaternaryammonium hydroxides. A person of ordinary skill in the art willrecognize that additional ranges of developer concentrations within theexplicit ranges above are contemplated and are within the presentdisclosure.

In addition to the primary developer composition, the developer cancomprise additional compositions to facilitate the development process.Suitable additives include, for example, dissolved salts with cationsselected from the group consisting of ammonium, d-block metal cations(hafnium, zirconium, lanthanum, or the like), f-block metal cations(cerium, lutetium or the like), p-block metal cations (aluminum, tin, orthe like), alkali metals (lithium, sodium, potassium or the like), andcombinations thereof, and with anions selected from the group consistingof fluoride, chloride, bromide, iodide, nitrate, sulfate, phosphate,silicate, borate, peroxide, butoxide, formate, oxalate,ethylenediamine-tetraacetic acid (EDTA), tungstate, molybdate, or thelike and combinations thereof. Other potentially useful additivesinclude, for example, molecular chelating agents, such as polyamines,alcohol amines, amino acids, carboxylic acids, or combinations thereof.If the optional additives are present, the developer can comprise nomore than about 10 weight percent additive and in further embodiments nomore than about 5 weight percent additive. A person of ordinary skill inthe art will recognize that additional ranges of additive concentrationswithin the explicit ranges above are contemplated and are within thepresent disclosure. The additives can be selected to improve contrast,sensitivity and line width roughness. The additives in the developer canalso inhibit formation and precipitation of metal oxide particles.

With a weaker developer, e.g., lower concentration aqueous developer,diluted organic developer or compositions in which the coating has alower development rate, a higher temperature development process can beused to increase the rate of the process. With a stronger developer, thetemperature of the development process can be lower to reduce the rateand/or control the kinetics of the development. In general, thetemperature of the development can be adjusted between the appropriatevalues consistent with the volatility of the solvents. Additionally,developer with dissolved coating material near the developer-coatinginterface can be dispersed with ultrasonication during development.

The developer can be applied to the patterned coating material using anyreasonable approach. For example, the developer can be sprayed onto thepatterned coating material. Also, spin coating can be used. Forautomated processing, a puddle method can be used involving the pouringof the developer onto the coating material in a stationary format. Ifdesired spin rinsing and/or drying can be used to complete thedevelopment process. Suitable rinsing solutions include, for example,ultrapure water, methyl alcohol, ethyl alcohol, propyl alcohol andcombinations thereof for negative patterning and ultrapure water forpositive patterning. After the image is developed, the coating materialis disposed on the substrate as a pattern.

After completion of the development step, the coating materials can beheat treated to further condense the material and to further dehydrate,densify, or remove residual developer from the material. This heattreatment can be particularly desirable for embodiments in which theoxide coating material is incorporated into the ultimate device,although it may be desirable to perform the heat treatment for someembodiments in which the coating material is used as a resist andultimately removed if the stabilization of the coating material isdesirable to facilitate further patterning. In particular, the bake ofthe patterned coating material can be performed under conditions inwhich the patterned coating material exhibits desired levels of etchselectivity. In some embodiments, the patterned coating material can beheated to a temperature from about 100° C. to about 600° C., in furtherembodiments from about 175° C. to about 500° C. and in additionalembodiments from about 200° C. to about 400° C. The heating can beperformed for at least about 1 minute, in other embodiment for about 2minutes to about 1 hour, in further embodiments from about 2.5 minutesto about 25 minutes. The heating may be performed in air, vacuum, or aninert gas ambient, such as Ar or N₂. A person of ordinary skill in theart will recognize that additional ranges of temperatures and time forthe heat treatment within the explicit ranges above are contemplated andare within the present disclosure. Likewise, non-thermal treatments,including blanket UV exposure, or exposure to an oxidizing plasma suchas O₂ may also be employed for similar purposes.

With conventional organic resists, structures are susceptible to patterncollapse if the aspect ratio, height divided by width, of a structurebecomes too large. Pattern collapse can be associated with mechanicalinstability of a high aspect ratio structure such that forces, e.g.,surface tension, associated with the processing steps distort thestructural elements. Low aspect ratio structures are more stable withrespect to potential distorting forces. With the patternable coatingmaterials described herein, due to the ability to process effectivelythe structures with thinner layers of coating material, improvedpatterning can be accomplished without the need for high aspect ratiopatterned coating material. Thus, very high resolution features havebeen formed without resorting to high aspect ratio features in thepatterned coating material.

The resulting structures can have sharp edges with very low line-widthroughness. In particular, in addition to the ability to reduceline-width roughness, the high contrast also allows for the formation ofsmall features and spaces between features as well as the ability toform very well resolved two-dimensional patterns (e.g., sharp corners).Thus, in some embodiments, adjacent linear segments of neighboringstructures can have an average pitch (half-pitch) of no more than about60 nm (30 nm half-pitch), in some embodiments no more than about 50 nm(25 nm half-pitch) and in further embodiments no more than about 34 nm(17 nm half-pitch). Pitch can be evaluated by design and confirmed withscanning electron microscopy (SEM), such as with a top-down image. Asused herein, pitch refers to the spatial period, or the center-to-centerdistances of repeating structural elements, and as generally used in theart a half-pitch is a half of the pitch. Feature dimensions of a patterncan also be described with respect to the average width of the feature,which is generally evaluated away from corners or the like. Also,features can refer to gaps between material elements and/or to materialelements. In some embodiments, average widths can be no more than about25 nm, in further embodiments no more than about 20 nm, and inadditional embodiments no more than about 15 nm. Average line-widthroughness can be no more than about 5 nm, in some embodiments no morethan about 4.5 nm and in further embodiments from about 2.5 nm to about4 nm. Evaluating line-width roughness is performed by analysis oftop-down SEM images to derive a 3σ deviation from the mean line-width.The mean contains both high-frequency and low-frequency roughness, i.e.,short correlation lengths and long correlation lengths, respectively.The line-width roughness of organic resists is characterized primarilyby long correlation lengths, while the present organometallic coatingmaterials exhibit significantly shorter correlation lengths. In apattern transfer process, short correlation roughness can be smoothedduring the etching process, producing a much higher fidelity pattern. Aperson of ordinary skill in the art will recognize that additionalranges of pitch, average widths and line-width roughness within theexplicit ranges above are contemplated and are within the presentdisclosure.

Further Processing of Patterned Coating Material

After forming a patterned coating material, the coating material can befurther processed to facilitate formation of the selected devices.Furthermore, further material deposition, etching and/or patterninggenerally can be performed to complete structures. The coating materialmay or may not ultimately be removed. The quality of the patternedcoating material can in any case be carried forward for the formation ofimproved devices, such as devices with smaller foot prints and the like.

The patterned coating material forms openings to the underlyingsubstrate, as shown for example in FIGS. 3 and 4. As with conventionalresists, the patterned coating material forms an etch mask which can beused to transfer the pattern to selectively remove an underlying thinfilm. Referring to FIG. 7, underlying thin film 103 (see FIG. 6) ispatterned leaving features 152, 154, 156 respectively under condensedregions 110, 112, 114. Compared with conventional polymer resists, thematerials described herein can provide significantly greater etchresistance. Similar processing can be undertaken with the mask patternshown in FIGS. 5 and 6 with corresponding shifting of the patternedstructures that follow directly from the alternative mask pattern.

Alternatively or additionally, the deposition of a further materialaccording to the mask pattern can alter the properties of the underlyingstructure and/or provide contact to the underlying structure. Thefurther coating material can be selected based on the desired propertiesof the material. In addition, ions can be selectively implanted into theunderlying structure through openings in the mask, as the density of thepatterned inorganic coating material can provide a high implantresistance. In some embodiments, the further deposited material can be adielectric, a semiconductor, a conductor or other suitable material. Thefurther deposited material can be deposited using suitable approaches,such as solution based approaches, chemical vapor deposition (CVD),sputtering, physical vapor deposition (PVD), or other suitable approach.

In general, a plurality of additional layers can be deposited. Inconjunction with the deposition of a plurality of layers, additionalpatterning can be performed. Any additional patterning, if performed,can be performed with additional quantities of the coating materialsdescribed herein, with polymer-based resists, with other patterningapproaches or a combination thereof.

As noted above, a layer of coating (resist) material followingpatterning may or may not be removed. If the layer is not removed, thepatterned coating (resist) material is incorporated into the structure.For embodiments in which the patterned coating (resist) material isincorporated into the structure, the properties of the coating (resist)material can be selected to provide for desired patterning properties aswell as also for the properties of the material within the structure.

If it is desired to remove the patterned coating material, the coatingmaterial functions as a conventional resist. The patterned coatingmaterial is used to pattern a subsequently deposited material prior tothe removal of the resist/coating material and/or to selectively etchthe substrate through the spaces in the condensed coating material. Thecondensed coating material can be removed using a suitable etchingprocess. Specifically, to remove the condensed coating material, a dryetch can be performed, for example, with a BCl₃ plasma, Cl₂ plasma, HBrplasma, Ar plasma or plasmas with other appropriate process gases.Alternatively or additionally, a wet etch with, for example, an aqueousacid or base, such as HF(aq), or buffered HF(aq)/NH₄F or oxalic acid canbe used to remove the patterned coating material. Referring to FIG. 8,the structure of FIG. 8 is shown after removal of the coating material.Etched structure 150 comprises substrate 102 and features 152, 154, 156.

The metal oxo/hydroxo based coating materials are particularlyconvenient for performing multiple patterning using a thermal freezeprocess, as described generally with conventional resists in P.Zimmerman, J. Photopolym. Sci. Technol., Vol. 22, No. 5, 2009, p. 625. Adouble patterning process with a “thermal freeze” is outlined in FIG. 9.In the first step, the coating material is formed into a pattern 160 onsubstrate 162 using a lithographic process and development as describedwith respect to FIGS. 3 and 4. A heating step 164 is performed to removesolvent and condense the coating material, which may or may not involvefull oxide formation. This heating step is equivalent to thepost-development heating step described in the Development sectionabove. This “thermal freeze” process makes the coating materialinsoluble to a subsequent deposition of a second layer of the coatingmaterial. A second lithographic and development step 166 is performed toform a double patterned structure 168 on substrate 162. After an etchstep 170, the product double patterned structure 172 is formed. Notethat it is straightforward to extend this process to multiple coat andpattern steps, and such extensions are contemplated and are within thepresent disclosure. With respect to multiple patterning, a significantdifference between the inorganic coating materials described herein andconventional organic resists is that organic resists remain soluble inconventional resist casting solvents even after a thermal bake. Theresist materials described herein can be condensed with a thermal bakesuch that they are not soluble in organic solvents and subsequentcoating layers can be applied.

EXAMPLES Example 1 Hydrolysate of t-BuSn(NEt₂)₃

This example describes the preparation of a hydrolysate precursorsolution from t-butyl tris(diethylamido)tin.

A hydrolysate oxide hydroxide product with the nominal formulat-BuSnO_((3/2−x/2))(OH)_(x), (where 0>x<3) (1) was prepared from t-butyltris(diethylamido)tin (2), which was synthesized according to the methodreported in Hanssgen, D.; Puff, H.; Beckerman, N. Journal ofOrganometallic Chemistry, 293, 1985, 191-195, which is incorporatedherein by reference. A gas-tight syringe was used to steadily (˜125μL/s) add 4.4 g of t-butyl tris(diethylamido)tin to 150 mL of DI H₂O (18MΩ), forming an immediate precipitate that was allowed to stand for 5minutes. The resulting slurry was stirred for 30 minutes and thensuction filtered through no. 1 filter paper (Whatman). The resultingsolid was rinsed 3 times with 50-mL portions of DI H₂O. Solids retainedafter filtration and rinsing were dried under vacuum (˜5 torr) for 8 hat room temperature to yield 1.9 g of powdered solid of hydrolysate 1.

Elemental analyses of the powder sample by Microanalysis, Inc.,Wilmington, Del. yielded 22.43% C, 4.79% 14, and 0.11% N (mass). Theseresults are consistent with a composition ratio of 1 t-butyl:1 Sn(expected: 23.01% C, 4.83% 14, 0.0% N). The N content indicates completeremoval of diethylamine upon hydrolysis of t-butyltris(diethylamido)tin. Thermogravimetric-Mass Spectrometry analyses,which are performed in dry air on powders prepared by the sameprocedure, are likewise consistent with an approximate empiricalformulation (C₄H₉)SnOOH for hydrolysate as shown in FIGS. 10 and 11.Stepwise dehydration (50-150° C., ˜96% residual weight) anddealkylkation/combustion (200-500° C., ˜73%) are observed with a finalresidual weight corresponding to the expected SnO₂ product.

Example 2 Hydrolysate of i-PrSnCl₃

This example describes the preparation of a hydrolysate precursorsolution from i-propyltin trichloride.

The hydrolysate oxide hydroxide product (i-PrSnO_((3/2−x/2))(OH)_(x),where 0<x<3) (3) of i-propyltin trichloride (4, i-PrSnCl₃, Gelest) wasprepared by rapidly adding 6.5 g of compound i-propyltin trichloride to150 mL of 0.5-M NaOH (aq) with vigorous stirring, immediately producinga precipitate. The resulting mixture was stirred for 1 h at roomtemperature and then filtered with suction through no. 1 filter paper(Whatman). The retained solids were washed three times with ˜25-mLportions of DI H₂O and then then dried for 12 h under vacuum (˜5 torr)at room temperature.

Elemental analysis (18.04% C, 3.76% H, 1.38% Cl; Microanalysis, Inc.;Wilmington, Del.) of the dried powder, hydrolysate of i-propyltintrichloride, indicated substantial removal of chloride ions occurs uponhydrolysis of i-propyltin trichloride and an approximate hydrolysateempirical formula of i-PrSnO_((3/2−x/2))(OH)_(x) where x≈1. (Calculatedfor C₃H₈O₂Sn: 18.50% C, 4.14% 14, 0.00% Cl). The results are consistentwith the approximate empirical formula (C₃H₇)SnOOH for hydrolysate ofi-propyltin trichloride.

Example 3 Preparation of Photoresist Solutions

This example describes the preparation of photoresist solutions from thehydrolysate precursors.

A solution of compound 1 (Example 1) was prepared by adding 0.1 g of drypowder to 10 mL of methanol (ACS, 99.8%) while stirring to form amixture with a Sn concentration of ˜0.05 M. After stirring for 24 h, themixture was filtered through a 0.45-μm PTFE syringe filter to removeinsoluble material. Dynamic light scattering (DLS) analysis of theresulting precursor solution, performed using a Möbius instrument (WyattTechnology), is consistent with a unimodal mass weighted distribution ofclusters with a mean diameter of ˜1.9 nm, as shown in FIG. 12. Arepresentative time correlation function providing such a particle sizedistribution is shown in FIG. 13.

Nuclear Magnetic Resonance (NMR) spectroscopy was performed on similarsolutions prepared in d₄-methanol using a Bruker Avance-III-HD 600 MHzSpectrometer equipped with a Bruker Prodigy™ CryoProbe. A representative¹¹⁹Sn spectrum is shown in FIG. 14, and a representative ¹H spectrum isshown in FIG. 15. Two primary sets of proton resonances are observed,each consisting of a stronger (1.58, 140 ppm) and weaker (1.55, 1.37ppm) resonance. These locations and integrated intensities areapproximately consistent with the expected chemical shift of the methylprotons on —C(CH₃)₃ ligands bound to five- and six-coordinate tin atomsin a closo-type dodecameric cluster [(t-BuSn)₁₂O₁₄(OH)₆]⁺² or closelyrelated chemical environment. Resonances centered at 3.33, and 4.90 ppmare attributed to methanol CH₃ and OH protons. Two sets ofclosely-spaced ¹¹⁹Sn resonances are observed at −333.86 and −336.10 ppm,and at −520.33 and −521.48 ppm. These results similarly approximateexpected shifts for the two tin environments in the cationic dodecamerclusters, as described for (n-BuSn)₁₂ clusters by Eychenne-Baron, etal., Organometallics 19, 2000, 1940-1949., incorporated herein byreference.

Electrospray Ionization Mass Spectroscopy (ESI-MS) was used tocharacterize methanol solutions of the same hydrolysate. Representativepositive-ion mode mass spectra are presented in FIG. 16. Two primarycationic species are observed in the spectra. One, at a mass to charge(m/z) ratio of 1219, and a second, stronger signal at m/z=2435. Thesem/z ratios are attributed to the presence of a doubly charged([(t-BuSn)₁₂O₁₄(OH)₆]⁺² calculated=1218) and singly charged(deprotonated, [(t-BuSn)₁₂(O₁₅(OH)₅]⁺ m/z=2435) cationic dodecamericspecies in the methanol solutions of the hydrolysate. Surrounding thepeak at m/z 2436 are a number of shoulder and satellite peaks, that mayrepresent the presence of methoxo and solvated or hydrated derivativesof the primary dodecameric species, and are presumed to correspond tothe closely related ¹¹⁹Sn and ¹H resonances observed via NMR.

A solution of compound 3 (Example 2) was prepared by adding 0.16 g ofdry powder to 10 mL of 4-methyl-2-pentanol (Alfa-Aesar, 99%) whilestirring to form a mixture with a Sn concentration of ˜0.08 M. Afterstirring for 2 h, the mixture was dried overnight with activated 4Amolecular sieves to remove residual water, and then filtered through a0.45 μm PTFE syringe filter to remove insoluble material.

Example 4 Resist Coating, Film Processing, Negative Tone Imaging

This example demonstrates the formation of a resist pattern based onnegative tone imaging with extreme ultraviolet radiation exposure.Branched alkyltin oxide hydroxide photoresists were coated on siliconwafers and negative-tone characteristic contrast curves generated usingEUV radiation.

Silicon wafers (100-mm diameter) with a native-oxide surface were usedas substrates for thin-film deposition. Si substrates were treated witha hexamethyldisilazane (HMDS) vapor prime prior to resist deposition.Silicon wafers (100-mm diameter) with a native-oxide surface were usedas substrates for thin-film deposition. Si substrates were treated witha hexamethyldisilazane (HMDS) vapor prime prior to resist deposition.i-Propyl and t-butyl tin oxide hydroxide photoresist solutions wereprepared as described in Example 3, and diluted to ˜0.06 and 0.05 M,respectively. Precursor solutions of an n-butyltin oxide hydroxide(n-BuSnO_((3/2−x/2))(OH)_(x)) resist solutions (0.057 M Sn) wereprepared as described in the '524 application cited above. Precursorsolutions were spin-coated on Si substrates and baked for 2 minutes atthe indicated rpm/temperature to form alkyltin oxide hydroxide resistthin films: 1500 rpm/80° C. (^(i)Pr-); 1800 rpm/100° C. (^(n)Bu-); 2000rpm/100° C. (^(t)Bu-).

A linear array of 50 circular pads ˜500 um in diameter were projected onthe wafer using EUV light (Lawrence Berkeley National Laboratory MicroExposure Tool, MET). Pad exposure times were modulated to deliver anincreasing EUV dose (7% exponential step) to each pad. Resist andsubstrate were then subjected to a post-exposure bake (PEB) on ahotplate for 2 min at 100-200° C. The exposed films were dipped in2-heptanone for 15 seconds and rinsed an additional 15 seconds with thesame developer to form a negative tone image, i.e., unexposed portionsof the coating were removed. n-Butyltin oxide hydroxide resist filmswere further rinsed 30 s in DI H₂O. A final 150° C., 2 minutes hotplatebake was performed to complete the process. Residual resist thicknessesof the exposed pads were measured using a J. A. Woollam M-2000Spectroscopic Ellipsometer. The measured thicknesses were normalized tothe maximum measured resist thickness and plotted versus the logarithmof exposure dose to form characteristic curves for each resist at aseries of PEB temperatures. The maximum slope of the normalizedthickness vs log dose curve is defined as the photoresist contrast (γ)and the dose value at which a tangent line drawn through this pointequals 1 is defined as the photoresist dose-to-gel, (D_(g)). In this waycommon parameters used for photoresist characterization may beapproximated following Mack, C. Fundamental Principles of OpticalLithography, John Wiley & Sons, Chichester, U.K; pp 271-272, 2007,incorporated herein by reference.

By plotting γ versus D_(g) for each resist, a clear relationship betweendecreasing dose and contrast is illustrated as the PEB temperature isincreased for each resist (FIG. 17). It is found that both branchedalkyltin oxide hydroxide resists tested here have better contrast thanthe n-butyltin oxide hydroxide-based resist, and preserve equivalent orbetter contrast at lower dose (as modulated by PEB) when developed in2-heptanone.

The improved sensitivity and contrast obtained from branched alkyltinoxide hydroxide photoresists were similarly used to generatehigh-resolution patterns by exposure to EUV radiation. The solution ofcompound 1 from Example 3 was diluted with methanol to ˜0.03 M Sn thenspin-coated on the substrate at 2000 rpm and baked on a hotplate for 2minutes at 100° C. Film thickness following coating and baking wasmeasured via ellipsometry to be ˜23 nm.

The coated substrate was exposed to extreme ultraviolet radiation(Lawrence Berkeley National Laboratory Micro Exposure Tool). A patternof 17-nm lines on a 34-nm pitch was projected onto the wafer using13.5-nm wavelength radiation, dipole illumination, and a numericalaperture of 0.3 at an imaging dose of 43 mJ/cm². The patterned resistand substrate were then subjected to a post-exposure bake (PEB) on ahotplate for 2 minutes at 175° C. The exposed film was then dipped in2-heptanone for 15 seconds, rinsed an additional 15 seconds with thesame developer, and finally rinsed for 30 seconds with DI H₂O to form anegative tone image, i.e., unexposed portions of the coating wereremoved. A final 5-minute hotplate bake at 150° C. was performed afterdevelopment. FIG. 18 exhibits SEM images of the resulting 15.4-nm resistlines patterned on a 34-nm pitch with a calculated line-width roughness(LWR) of 4.6 nm.

The solution of i-PrSnO_((3/2−x/2))(OH)_(x) (compound 3 from Example 2)was used in a similar way to realize high-resolution patterning via EUVexposure. Solution of 3 from Example 3 was diluted in4-methyl-2-pentanol to ˜0.06 M Sn, and spin-coated on a second Sisubstrate at 1500 rpm and baked on a hotplate for 2 minutes at 80° C.Film thickness following coating and baking was measured viaellipsometry to be ˜19 nm. A bright-field pattern of 22-nm contact holeson a 44 nm pitch with a +20% bias was projected onto the wafer usingquadrupole illumination at an imaging dose of 36 mJ/cm². The patternedresist and substrate were then subjected to a PEB for 2 minutes at 150°C. The exposed film was then dipped in 2-octanone for 15 seconds andrinsed with 2-octanone for an additional 15 seconds to form a negativetone image with unexposed portions of the coating removed, leaving apattern of contact holes. A final 5-minute hotplate bake at 150° C. wasperformed after development. FIG. 19 exhibits SEM images of theresulting 22-nm holes patterned on a 44-nm pitch.

Example 5 Preparation of Photoresist Solutions with Mixed Alkyl Ligands

This Example describes the formulation of precursor solutions comprisingmixed alkyl ligands, and the effectiveness of these formulations forpatterning are described in the following example.

A t-butyltin oxide hydroxide hydrolysate (1) was prepared from t-butyltris(diethylamido)tin following the method described above in Example 1.A gas-tight syringe was used to add 4.4 g (11 mmol) of t-butyltris(diethylamido)tin to 150 mL of DI H₂O (18 MΩ), forming an immediateprecipitate that was allowed to stand for 5 minutes. The resultingslurry was stirred for 30 minutes and then suction filtered through no.1 filter paper (Whatman) and rinsed 3 times with 60-mL portions of DIH₂O. Solids retained after filtration and rinsing were dried undervacuum (˜5 torr) for 17 hours at room temperature to yield 1.85 g ofpowdered solid of hydrolysate t-butyltin oxide hydroxide (1).

An i-propyltin oxide hydroxide hydrolysate (3) was similarly prepared bythe method described above in Example 2. A 9.65 g (36 mmol) quantity ofi-propyltin trichloride (i-PrSnCl₃, Gelest) was rapidly added to 220 mLof 0.5-M NaOH (aq) while stirring vigorously, immediately producing aprecipitate. The resulting mixture was stirred for 1.25 hours at roomtemperature and then filtered with suction through two no. 5 filterpapers (Whatman). The retained solids were washed 3 times with ˜30-mLportions of DI H₂O and then then dried for 16 hours under vacuum (˜5torr) at room temperature.

Separate solutions of t-butyltin oxide hydroxide hydrolysate (1) andi-propyltin oxide hydroxide hydrolysate (3) were prepared from therespective powders. A 1.04 g quantity of dried powder t-butyltin oxidehydroxide hydrolysate was added to 100 mL methanol (ACS, 99.8%) andstirred for 24 hours, whereupon the mixture was syringe filtered througha 0.45-um PTFE filter to remove insoluble particles. The residual massof a sample following solvent evaporation and subsequent thermaldecomposition of the residual solids at 700° C. in air was consistentwith an initial Sn concentration of 0.035 M assuming stoichiometricconversion to SnO₂. A solution of i-propyltin oxide hydroxidehydrolysate (3) was prepared by adding 3.129 g of dry powder to 80 mL of4-methyl-2-pentanol (Alfa-Aesar, 99%) while stirring. After stirring for6 hours, the mixture was dried 60 hours over activated 4A molecularsieves, then vacuum filtered through a 0.2-um PTFE membrane filter toremove insoluble material. The Sn concentration of the solution wasfound to be 0.16 M via thermal decomposition to the oxide.

Photoresist formulations A-F (Table 2) were prepared by mixing themethanol solution of t-butyl tin oxide hydroxide hydrolysate (1) withthe 4-methyl-2-pentanol solution of i-propyl tin oxide hydroxidehydrolysate (3), and diluting the resulting mixture with pure solventsaccording to the volumes specified in Table 2. The resulting solutionsare characterized as a blend of i-PrSnO_((3/2−x/2))(OH)_(x) andt-BuSnO_((3/2−x/2))(OH)_(x) hydrolysates, where the fraction oft-BuSnO_((3/2−x/2))(OH)_(x) is expressed relative to the total Snconcentration.

TABLE 2 Volume Added (mL) t-Bu—Sn 4-methyl Solution Solution relative toFormulation Methanol 2-pentanol 3 1 Total Sn (%) A 0 0 0 5 100 B 0 0.750.5 3.75 62 C 0 0.45 0.8 3.75 50 D 1.033 0.517 1.15 2.3 30 E 0 1.5 1.5 222 F 0 2.75 2.25 0 0

Example 6 Resist Coating, Film Processing, Negative Tone Imaging withMixed Alkyl Ligand Precursors

Mixed-ligand organotin oxide hydroxide photoresists were used togenerate negative-tone patterns by exposure to extreme ultravioletradiation. This Example explores patterning using the precursorsolutions from Example 5 having mixed alkyl ligands.

Silicon wafers (100-mm diameter) with a native-oxide surface were usedas substrates for thin-film deposition. Si substrates were treated witha hexamethyldisilazane (HMDS) vapor prime prior to resist deposition.Resist formulations A-F from Example 5 were spin-coated on substrates at2000-2500 rpm and baked on a hotplate for 2 minutes at 100° C. Filmthickness following coating and baking was measured via ellipsometry tobe ˜30 nm. The coated substrates were exposed to extreme ultravioletradiation (Lawrence Berkeley National Laboratory Micro Exposure Tool). Apattern of 17-nm lines and spaces on a 34-nm pitch was projected ontothe wafer using 13.5-nm wavelength radiation, dipole illumination, and anumerical aperture of 0.3. The patterned resist and substrate were thensubjected to a post-exposure bake (PEB) on a hotplate for 2 minutes at170° C. The exposed film was then dipped in 2-heptanone for 15 secondsand rinsed an additional 15 seconds with the same developer to form anegative tone image, i.e., unexposed portions of the coating wereremoved. A final 5-minute hotplate bake at 150° C. was performed afterdevelopment.

FIG. 20 exhibits SEM images of the resulting resist lines patterned on a34-nm pitch. SuMMIT analysis software (EUV Technology Corporation) wasused to extract resist critical dimension (CD) and line-width-roughness(LWR) from SEM images of 17 hp lines patterned using resist formulationA-F. A plot of LWR and Dose to size (E_(size)) for each formulation isshown in FIG. 21. A clear trend of decreasing dose (circular dots) isobserved across the formulations as the fraction oft-BuSnO_((3/2−x/2))(OH)_(x) is increased. Moreover, LWR (triangulardots) in FIG. 21 for blended formulations are substantially lower thanpure t-BuSnO_((3/2−x/2))(OH)_(x) and i-PrSnO_((3/2−x/2))(OH)_(x)formulations A and F, respectively.

Example 7 Preparation of an Iso-propyltin Hydroxide Oxide HydrolysateVia an Iso-propyl Tris(dimethylamido)tin Precursor

A water-reactive precursor, isopropyl tris(dimethylamido)tin,(i-PrSn(NMe₂)₃), was synthesized under inert atmosphere and subsequentlyhydrolysed by two methods using 1) atmospheric moisture and 2) liquidH₂O, to form an i-PrSnO_((3/2−x/2))(OH)_(x) hydrolysate.

Under argon, a 1 L Schlenk-adapted round bottom flask was charged withLiNMe₂ (81.75 g, 1.6 mol, Sigma-Aldrich) and anhydrous hexanes (700 mL,Sigma-Aldrich) to form a slurry. A large stir bar was added and thevessel sealed. An addition funnel under positive argon pressure wascharged with i-PrSnCl₃, (134.3 g, 0.5 mol, Gelest) via syringe andattached to the reaction flask. The flask was cooled to −78° C. and thei-PrSnCl₃ added dropwise over a period of 2 hours. The reaction wasallowed to come to room temperature overnight while stirring, and thesolid precipitates allowed to settle. After settling, the reactionsolution was filtered under positive argon pressure through an in-linecannula filter. The solvent was removed under vacuum and the residuedistilled under reduced pressure (50-52° C., 1.4 mmHg) to give a paleyellow liquid (110 g, 75% yield). ¹H and ¹¹⁹Sn NMR spectra of thedistillate in a C₆D₆ solvent collected on a Bruker DPX-400 (400 MHz, BBOprobe) spectrometer are shown in FIGS. 22 and 23, respectively. Observed¹H resonances, as shown in FIG. 22, (s, 2.82 ppm, —N(CH₃)₂; d 1.26 ppm,—CH₃; m, 1.60 ppm, —CH) match the predicted spectra for ^(i)PrSn(NMe₂)₃.The primary ¹¹⁹Sn resonance, as shown in FIG. 23, at −65.4 ppm isconsistent with a major product with a single tin environment, with achemical shift comparable to reported monoalkyltin amido compounds.

An i-propyltin oxide hydroxide hydrolysate was prepared from thei-propyl tris(dimethylamido)tin, (i-PrSn(NMe₂)₃), via H₂O hydrolysisusing two different methods.

Method 1:

A gas-tight syringe was used to add 23.4 g (79.6 mmol) of i-propyltris(dimethylamido)tin, (i-PrSn(NMe₂)₃) to 150 mL of n-hexanes (HPLCGrade, >99.5% Hexanes, >95% n-Hexane), forming an opaque suspension thatwas stirred for 5 minutes in air, then poured in equal volumes into six150 mm diameter petri dishes. The suspensions were allowed to react withatmospheric moisture while the solvent evaporated in air for 1.5 hours,leaving a crude solid that was collected, combined, and dried undervacuum for 15 hours to yield 15.8 g of solid hydrolysate (compound 3,Example 2). Elemental analyses (UC Berkeley Microanalytical Facility) ofa hydrolysate powder prepared by the same procedure returned acomposition of 18.91% C, 4.24% H, and 0.51% N (mass), consistent withsubstantial hydrolysis of dimethylamido ligands and evaporation of theresultant alkyl amine. The results are consistent with calculated valuesfor C₃H₈O₂Sn: 18.50% C, 4.14% H, 0.00% N, and 60.94% Sn, mass).Thermogravimetric analysis (FIG. 24) of the same sample in dry air isindicative of a Sn composition of ˜60% (mass) based on the residualweight at 500° C. (75.9%) assuming complete decomposition to SnO₂. Themass spectral analysis of the same decomposition (FIG. 25) indicates thepresence of —C₃H₆. Taken together, these results agree with an empiricalcomposition of i-PrSnSnO_((3/2−x/2))(OH)_(x) where x≈1, and the possiblepresence of a small amount of residual dimethyl amido.

Method 2:

A gas-tight syringe was used to rapidly add 1.0 g (3.4 mmol) of i-propyltris(dimethylamido)tin, (i-PrSn(NMe₂)₃) directly to 15 mL DI H₂O (18.2MΩ) with vigorous stirring to form a slurry that was stirred for anadditional 60 minutes. This slurry was then vacuum filtered through a0.7-μm filter and the retained solids washed with 10 mL DI H₂O. Thesolid was then collected and dried under vacuum for 16 hours to yield0.7 g of solid hydrolysate. Thermogravimetric analyses, performed in dryair on hydrolysate powders prepared by the same procedure (FIG. 26), aresimilarly consistent with the empirical composition of 3 (Example 2),i-PrSnSnO_((3/2−x/2))(OH)_(x) where x≈1. Weight losses attributed tostepwise dehydration (50-175° C., ˜95.7% residual weight) anddealkylkation/combustion (200-500° C., ˜77% residual weight) areobserved as expected on the basis of complete decomposition of 3 toSnO₂.

Example 8 Trace-metals Analysis of Organotin Oxide Hydroxide PhotoresistSolutions

A resist precursor solution was prepared by adding 15.8 g of driedpowder, prepared according to Method 1 in the preceding example, to 810mL 4-methyl-2-pentanol (High Purity Products), and stirring for 24 h.Following stirring, the mixture was suction filtered through a 0.22-μmPTFE filter to remove insoluble material. The residual mass of a samplefollowing solvent evaporation and subsequent calcination of the solid at700° C. in air was consistent with an initial Sn concentration of 0.072M assuming stoichiometric conversion to SnO₂.

Trace-metal concentrations in the resist precursor solution above wereevaluated relative to a hydrolysate prepared using aqueous sodiumhydroxide and i-propyltin trichloride. The 0.072-M solution preparedabove, was further diluted to 0.042 M (Sn) with 4-methyl-2-pentanol. Asecond i-propyltin oxide hydroxide precursor solution was prepared byhydrolysis of i-PrSnCl₃ with aqueous NaOH as described in Example 2, anddiluted to 0.42 M Sn with the same high-purity 4-methyl-2-pentanol.Aliquots of both solutions were analyzed using inductively coupledplasma mass spectroscopy (ICP-MS, Balazs Nanoanalysis, Fremont, Calif.)to determine the concentration of 22 metals with a lower detection limit(LDL) of 10 parts per billion (ng/g). The results of these analyses arepresented in Table 3. In both cases the concentration of all analyzedmetals except sodium (Na) was <10 ppb. The resist solution (A)containing the hydrolysate prepared with NaOH (aq) was found to contain34,000 ppb residual sodium, even after three washings with 18 M) DI H₂O.In contrast, the resist solution (B) prepared from the hydrolysate ofi-propyl (tris)dimethylamido tin was found to contain <10 ppb Na, asanticipated by the alkali-free hydrolysis.

Trace metal concentrations in i-PrSnSnO_((3/2−x/2))(OH)_(x) photoresistprecursor solutions as measured by ICP-MS with an LDL of 10 ppb areshown in Table 3.

TABLE 3 Concentration, ppb (ng/g) Resist Resist Precursor A Precursor Bi-PrSnCl₃/ i-PrSn(NMe₂)₃/ Metal NaOH Air Aluminum (Al) <10 <10 Arsenic(As) <10 <10 Barium (Ba) <10 <10 Cadmium (Cd) <10 <10 Calcium (Ca) <10<10 Chromium (Cr) <10 <10 Cobalt (Co) <10 <10 Copper (Cu) <10 <10 Gold(Au) <10 <10 Iron (Fe) <10 <10 Lithium (Li) <10 <10 Magnesium (Mg) <10<10 Manganese (Mn) <10 <10 Nickel (Ni) <10 <10 Palladium (Pd) <10 <10Potassium (K) <10 <10 Silver (Ag) <10 <10 Sodium (Na) 34,000 <10Titanium (Ti) <10 <10 Tungsten (W) <10 <10 Vanadium (V) <10 <10 Zinc(Zn) <10 <10

Example 9 Film Coating, Processing, and Negative Tone Imaging of aPhotoresist with Low Trace-Metal Contamination

Silicon wafers (100-mm diameter) with a native-oxide surface were usedas substrates for thin-film deposition. Si substrates were treated witha hexamethyldisilazane (HMDS) vapor prime prior to resist deposition.The 0.072 M resist solution from Example 8 was dispensed through a 0.45nm syringe filter onto a substrate, spin-coated at 1500 rpm, and bakedon a hotplate for 2 min at 100° C. Film thickness following coating andbaking was measured via ellipsometry to be ˜25 nm. The coated substratewas exposed to extreme ultraviolet radiation (Lawrence Berkeley NationalLaboratory Micro Exposure Tool). A pattern of 17-nm lines and spaces ona 34-nm pitch was projected onto the wafer using 13.5-nm wavelengthradiation, dipole illumination, and a numerical aperture of 0.3. Thepatterned resist and substrate were then subjected to a post-exposurebake (PEB) on a hotplate for 2 min at 180° C. The exposed film was thendipped in 2-heptanone for 15 seconds and rinsed an additional 15 secondswith the same developer to form a negative tone image, i.e., unexposedportions of the coating were removed. A final 5-minute hotplate bake at150° C. was performed after development. FIG. 27 shows an SEM image ofthe resulting resist line/space pattern on the substrate defined with animaging dose of 60 mJ cm⁻², 14.5 nm resist lines patterned on a 34 nmpitch with an LWR of 2.9 nm.

Example 10 Preparation of an i-Propyltin Hydrolysate Via Hydrolysis ofIso-propyltin Trichloride with an Aqueous Organic Base

A hydrolysate of i-PrSnCl₃ was prepared by rapidly adding 6.5 g (24mmol) of compound 4 i-PrSnCl₃ to 150 mL of 0.5-M aqueous tetramethylammonium hydroxide (TMAH) while stirring vigorously, immediatelyproducing a precipitate. TMAH is free of metal cations in the formula sothat it can be introduced with low metal contamination. The resultingmixture was stirred for 1 hour at room temperature and then filteredwith suction through no. 1 filter paper (Whatman). The retained solidswere washed three times with ˜25-mL portions of DI H₂O and then thendried for 12 hours under vacuum (˜5 torr) at room temperature. Elementalanalysis (18.67% C, 4.22% H, 0.03% N, 0.90% Cl; Microanalysis, Inc.;Wilmington, Del.) of the dried powder hydrolysate, was consistent withsubstantial removal of chloride ions upon hydrolysis and rinsing, andagain in agreement with the general stoichiometryi-PrSnSnO_((3/2−x/2))(OH)_(x) where x≈1. (Calculated for C₃H₈O₂Sn:18.50% C, 4.14% H, 0.00% N, 0.00% CO. TGA-MS analyses, (dry air) ofhydrolysate powders prepared by the same procedure (FIGS. 28 and 29),are likewise consistent with the same. Weight losses attributed tostepwise dehydration (50-175° C., ˜97.0% residual weight) anddealkylkation/combustion (200-500° C., ˜77.5% residual weight) areobserved as expected on the basis of complete decomposition of to SnO₂.While this experiment was not conducted to specifically test for lowmetal contamination, the experiment is designed to indicate thecapability for the product t-amyltin oxide hydroxide to be synthesizedwith low metal contamination as demonstrated in companion examplesherein.

Example 11 Preparation of an Alklytin Hydroxide Oxide Hydrolysate ViaAqueous Hydrolysis of an Alkyltin tris(alkynide)

A t-amyl tin hydroxide oxide hydrolysate, t-AmylSnO_((3/2−x/2)) (0<x<3)(compound 6), was prepared via aqueous hydroloysis of(1,1-dimethylpropyl)tin tris(phenylacetylide), t-AmylSn(C≡CPh)₃(compound 7)

Tin tetra(phenylacetylide), Sn(C≡CPh)₄, compound 8 was synthesized asreported in Levashov, A. S.; Andreev, A. A.; Konshin, V. V. TetrahedronLetters, 56, 2015, 56, 1870-1872, incorporated herein by reference.Compound 7 was then prepared via transmetalation of compound 8 by amodification of the method of Jaumier, et al. (Jaumier P.; Jousseaume,B.; Lahcini, M. Angewandte Chemie, International Edition, 38, 1999,402-404, incorporated herein by reference): In a 150-mL flask,Sn(C≡CPh)₄ (9.53 g/19.33 mmol) was dissolved in anhydrous toluene (80mL). Nitrogen was then bubbled through the solution for 10 min, and thesolution cooled in an ice bath. 1,1-dimethylpropylmagnesium bromidesolution in ether (30 mL/1 N) was then added dropwise. The solution wasallowed to warm to room temperature and stirred for two hours. Thereaction mixture was then filtered through silica and condensed undervacuum. The resulting solid was sonicated in anhydrous hexanes,filtered, and the supernatant condensed under vacuum. The resulting waxysolid was then recrystallized from 20% aqueous methanol (v/v) at −10° C.over the course of 2 hours. Representative ¹¹⁹Sn and ¹H NMR spectra forcompound t-AmylSn(C≡CPh)₃ synthesized by this method are found in FIGS.30 and 31. FIG. 30 depicts the ¹H NMR spectrum. FIG. 31 depicts the¹¹⁹Sn NMR spectrum.

tert-Amyltin hydroxide oxide, t-AmylSnO_((3/2−x/2))(OH)_(x), where 0<x<3(compound 6), was prepared via hydrolysis of ^(t)AmylSn(C≡CPh)₃ with H₂Othrough an adaptation of the method Jaumier, et al. describe forunbranched alkyltin alkynides. Chemical Communications, 1998, 369-370,incorporated herein by reference. In a 50 mL flask, t-AmylSn(C≡CPh)₃ wasdissolved in tetrahydrofuran (20 mL/2% water) and 0.5 mL water. Thesolution was stirred at room temperature for two days and theprecipitate collected and dissolved in chloroform. The resultingsolution was filtered through a 0.2 μm PTFE filter, and the solventremoved under vacuum. Representative ¹¹⁹Sn (FIG. 32) and ¹H NMR spectra(FIG. 33) were collected in CDCl3. Observed ¹¹⁹Sn resonances at −340.65and −489.29 ppm are characteristic of the respective five andsix-coordinate tin atoms in closo-type dodecameric clusters of the form[(RSn)₁₂O₁₄(OH)₆](OH)₂. ¹H resonances are likewise indicative of thepresence of 1,1-dimethylpropyl ligands in the two chemical environments,and importantly only very weak phenyl resonances (7.29-7.60 ppm) areobserved relative to FIGS. 32 and 33, indicating near-completehydrolysis and removal of phenylacetylide ligands. While this experimentwas not conducted to specifically test for low metal contamination, theexperiment provides a synthetic approach that allows the productt-amyltin oxide hydroxide to be synthesized with low metal contaminationas demonstrated in companion examples herein.

Example 12 Resist Coating, Film Processing, Negative Tone Imaging withElectron Beam Exposure

t-BuSnO_((3/2−x/2))(OH)_(x) and i-PrSnSnO_((3/2−x/2))(OH)_(x) resistprecursor solutions were prepared as described in Example 3. Thesolutions were spin-coated and patterned using electron-beam lithographywith the process parameters summarized in Table 4. Silicon wafers (25×25mm²) with a native-oxide surface were used as substrates for thin-filmdeposition. Substrates were ashed for 1 min in a 25 W O₂ plasma at 15mTorr prior to resist coating. Precursor solutions were dispensedthrough a 0.45 nm syringe filter onto a substrate, spin-coated for 30 sat the indicated rpm, and baked on a hotplate for 2 min (post-applybake, PAB) at the indicated temperature. Film thickness followingcoating and baking was measured via ellipsometry. The coated substrateswere exposed to a 30-keV electron-beam rastered to form a line/spacepattern at the designated dose. The patterned resist and substrate werethen subjected to a post-exposure bake (PEB) on a hotplate for 2 min atthe temperature shown in Table 4. The exposed film was then dipped indeveloper for 15 seconds and rinsed an additional 15 seconds with thesame developer to form a negative tone image, i.e., unexposed portionsof the coating were removed. A final 5-minute hotplate bake at 150° C.was performed after development. FIG. 34 exhibits an SEM image of theresulting resist line/space patterns on the substrates at a pitch of32-nm (top) and 28-nm (bottom).

TABLE 4 Resist Precursor Formulation t-BuSnO_((3/2−x/2))(OH)_(x)i-PrSnSnO_((3/2−x/2))(OH)_(x) Solvent methanol 4-methyl-2-pentanolCoating Speed (rpm) 1500 2500 PAB temperature (° C.)  100  80 ResistFilm Thickness  40  31 (nm) PEB Temperature (° C.)  170  120 Developer2-heptanone 2-octanone Imaging Dose (μC cm⁻²) 1022  696 32/28 nm Pitch15.2/13.5 16.2/15.1 Resist Line Critical Dimension (nm)

Example 13 Positive Tone Imaging with EUV Exposure

A branched-alkyltin oxide hydroxide resist was used to generate positivetone images using EUV radiation. An i-PrSnO_((3/2−x/2))(OH)_(x)hydrolysate (compound 3) was prepared using Method 1 described inExample 7, and dissolved in 4-methyl-2-pentanol to produce ˜0.07 M Snprecursor solution. Silicon wafers (100 mm⁻ diameter) with anative-oxide surface were used as substrates for thin-film deposition. Ahexamethyldisilazane (HMDS) vapor prime was performed on the wafersprior to coating. The precursor solutions were dispensed via pipet ontothe substrate, spin-coated for 30 s at 1500 rpm, and baked on a hotplatefor 2 min at 100° C. Film thickness following coating and baking wasmeasured via ellipsometry to be ˜23 nm. EUV exposures were carried outon the Berkeley MET. A series of line and space patterns at varyingpitches were projected onto the wafer using 13.5-nm wavelength radiationand annular illumination at a numerical aperture of 0.3 and imaging doseof 25 mJ cm⁻². Immediately following exposure, the resist and substratewere baked a hotplate for 2 min at 150° C. in air.

The exposed film was dipped in a 0.52 M solution of aqueous NaOH for 15seconds and rinsed 15 seconds with H₂O to develop a positive tone image,i.e., exposed portions of the coating were removed. A final 5-minutehotplate bake at 150° C. was performed after development. SEM images ofpositive-tone resist lines patterned on a 100-nm, (a) and 60-nm (b)pitch are found in FIG. 35.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

What is claimed is:
 1. A coating solution consisting essentially of volatile organic solvent and an organometallic composition comprising a first organometallic compound represented by the formula RSnO_((3/2−x/2))(OH)_(x) where (0<x<3) with from about 0.0025M to about 1.0M tin in the solution, where R is an alkyl group bonded to the tin at a secondary or tertiary carbon atom.
 2. The coating solution of claim 1 wherein the first organometallic compound comprises tert-butyl tin oxide hydroxide (R=—C(CH₃)₃), iso-propyl tin oxide hydroxide (R=—CH(CH₃)₂), or mixtures thereof.
 3. The coating solution of claim 1 wherein the organometallic composition further comprises a second organometallic compound distinct from the first organometallic compound and represented by the formula R′SnO_((3/2−x/2))(OH)_(x) where (0<x<3) and R′ is a linear or branched alkyl.
 4. The coating solution of claim 1 wherein the organic solvent comprises an alcohol.
 5. A coating solution consisting essentially of an organic solvent and an organometallic composition comprising a first organometallic compound represented by the formula RSnO_((3/2−x/2))(OH)_(x) where (0<x<3), where R is an alkyl group, where the alkyl group is bonded to the tin at a secondary or tertiary carbon atom, and a second organometallic compound distinct from the first organometallic compound and represented by the formula R′SnO_((3/2−x/2))(OH)_(x) where (0<x<3), where R′ is a linear or branched alkyl group and wherein R and R′ are not the same.
 6. The coating solution of claim 5 wherein the first organometallic compound comprises tert-butyl tin oxide hydroxide (R=—C(CH₃)₃) or iso-propyl tin oxide hydroxide (R=—CH(CH₃)₂).
 7. The coating solution of claim 5 wherein R and R′ are each independently branched alkyl groups.
 8. The coating solution of claim 5 wherein the second organometallic compound represents at least about 8 mole percent of the organometallic compounds in the coating solution.
 9. The coating solution of claim 5 wherein the organometallic composition further comprises a third distinct organometallic compound represented by the formula R″SnO_((3/2−x/2))(OH)_(x) where (0<x<3), where R″ is a linear or branched alkyl group wherein the third organometallic compound represents at least about 8 mole percent of the organometallic compounds in the coating solution.
 10. The coating solution of claim 5 wherein the solvent comprises an alcohol and wherein the organometallic compounds result in a tin ion concentration from about 0.0025M to about1.5M and wherein the second organometallic compound represents at least about 8 mole percent of the organometallic compounds in the coating solution.
 11. A method for patterning a film on a substrate, the method comprising: exposing the film with patterned EUV doses of no more than about 80 mJ/cm² wherein the film has an average thickness from about 2 nm to about 50 nm and wherein the film comprises a first organometallic compound represented by the formula RSnO_((3/2−x/2))(OH)_(x) where (0<x<3), where R is an alkyl group bonded to the tin; and developing the film to form features at half-pitch no more than about 25 nm and linewidth roughness no more than about 5 nm.
 12. The method of claim 11 wherein the EUV dose is from about 12 mJ/cm² to about 75 mJ/cm².
 13. The method of claim 11 wherein the half-pitch is no more than about 18 nm.
 14. The method of claim 11 wherein R is bonded to the tin at a secondary or tertiary carbon.
 15. The method of claim 11 further comprising developing the film following exposure to form a negative image through the removal of unexposed portions of film.
 16. The method of claim 11 further comprising developing the film following exposure to form a positive image through the removal of exposed portions of film.
 17. A method for patterning an organometallic film on a substrate, the method comprising: exposing the organometallic film to patterned EUV radiation at a dose-to-gel value of no more than about 15 mJ/cm² to obtain a contrast of at least about
 6. 18. A patterned structure comprising a substrate having a surface and a coating associated with the surface wherein at least portions of the coating are represented by the formulation (R)_(z)SnO_(2−z/2−x/2)(OH)_(x) (z>0, x>0, and 0 <(x+z)<4), where R is an alkyl group bonded to the tin at a secondary or tertiary carbon atom, wherein the coating has an average thickness of no more than about 50 nm.
 19. The patterned structure of claim 18 wherein z is from about 0.25 to about
 3. 20. The patterned structure of claim 18 wherein the substrate comprises polymer, elemental silicon, silica, and/or another inorganic material.
 21. The patterned structure of claim 18 wherein the coating forms a pattern at least a portion of which forms features with a half-pitch of no more than about 25 nm. 